08 mercury 60hp on 15' aluminum, harf time matching up a prop

[Texasmark]

Ran some more numbers looking for your realistic rpm with your original setup.

Starting with your serial number pulled up ratio of 2.33, I will add your GPS corrected speed of 43.6., use current 19P and will maintain the 12% slip as that's what I had with my 90 on my 17' boat pictured in my Avatar at 50, and I suspect when you get me a shot of your wake, I'll estimate your slip to be in that range too. Those numbers will give me a place to start.

First shot, guessing 5500 rpm: 42 max, 37 actual........you can't get to your 43.6 from here.

2nd shot, backing into rpm: 6475..........hmmmmm real close to your earlier posted 6400 "no trim" numbers.

The prop in your pictures has some rake but no cupping. Cupping helps the blades to grip in high trim angles when the blades are near the surface. Just suppose, your best trim rpm was infact as high as it was because you were blowing out. You trimmed out till the boat achieved max speed before the speed started falling off because the prop was blowing out (sucking in air) which unloaded the engine allowing it to increase rpms.
--------------------------------------------------------------------------------------------------------------------------------------------------------------
This may be coming together after all.

If in fact you do have the 2.33 I'm going to bet that your Mini Tach is dead nuts on when it read 6400 and that you are over revving your engine with your current prop. However, with what I said earlier about light load vs loaded for ducks, you may want to leave it be and back off the throttle when running alone and light.


Assume you want to have 2 props for the 2 situations (possibly, we'll see if that'll work) then working on pulling the rpms down to 5500, run some prop pitch numbers:

RPM: 5500
Gear: 2.33
Slip: 12%
Speed 43.6
Prop: TBD: Calculator value = 22P. A 21, as you originally said........."I'll just put a 21 on it and go from there".......could be your answer after all. If you get the Turning Point Hustler alum. 21P, PN 21432111, which I boats sells for $115 with free shipping, the cupping of the prop will bring you up to the effective pitch of 22 and will hold better at high trim positions and in tight turns keeping your rpms in check. It also has porting which will give you a faster/stronger hole shot. Your current prop has some rake so the inherent rake in the Hustler should not make much, if any, of a change in performance.
-----------------------------

I don't think you will achieve your desired objective of 50+ with your 60 hp engine on that boat. I think you have done all that you can, running the Hustler 21 will pull in your rpms to where they belong and overall you will have a fine running hull.

I will stay with you on this as you accumulate more data, but I think in retrospect, it will prove out what has already been surmised.....................assuming your tach is if fact accurate and your gear ratio is infact, 2.33.

Will wait.

 

[Wood Slayer]

Mark,
I will be back to the house around 11am today. I went back onto boats.net website and looked at parts diagrams.
The gearcase shows two options:
1.83
2.33
I will mark my flywheel/prop with masking tape and get the accurate revolutions for us.
2nd: i emailed tiny tach, i gave them my motor info and requested to know what setup I need to use on the tach.
------
If in fact im already at or near optimal settings on my rig, im ok with that! Im also planning on haveing two props for this rig. A hunt/heavy load, and a fish/light load.
Again, im just wanting optimal settings and when I saw a 7200rpm with trim and 6400 no trim. I freaked out.
The boat does porpoise some, so I will weight down the front. Im working hard to get back out on the water today, between the 19p and 23p prop and a correct rpm data. Im certain we can narrow down what props to purchase.
Will be back shortly!

 

[Texasmark]

Mark,
I will be back to the house around 11am today. I went back onto ********** website and looked at parts diagrams.
The gearcase shows two options:
1.83
2.33
I will mark my flywheel/prop with masking tape and get the accurate revolutions for us.
2nd: i emailed tiny tach, i gave them my motor info and requested to know what setup I need to use on the tach.
------
If in fact im already at or near optimal settings on my rig, im ok with that! Im also planning on haveing two props for this rig. A hunt/heavy load, and a fish/light load.
Again, im just wanting optimal settings and when I saw a 7200rpm with trim and 6400 no trim. I freaked out.
The boat does porpoise some, so I will weight down the front. Im working hard to get back out on the water today, between the 19p and 23p prop and a correct rpm data. Im certain we can narrow down what props to purchase.
Will be back shortly!

As you probably know, Porposing is too much trim for the given speed. Either increase boat speed (probably can't) or tuck in trim till it quits. Yes moving something forward will work but you don't need to, trim reduction will work and work better. Anything you put forward pushes the bow down causing more of the hull to get wet which slows your speed. It's a toss which affects what how much, but tweaking the trim is the easiest......which yes, will also get you more wetted area and slow you slightly.

The 1.83 is for the standard LU. When looking up props, the 1.4 and optional 1.83 numbers occurred in the standard LU prop column, not the big foot.

 

[Wood Slayer]

I just confirmed, per two revolutions of the flywheel does not turn the prop 1 full time. So 2.33 L/U.
I also just recieved the setup info for the tiny tach. Future reference- attach the red wire on the lowest spark plug wire, just 1 full wrap- clostest to the ground wire.
Now im planning on getting on the water today about 2pm est. will keep you posted.

 

[Texasmark]

While I'm waiting, the last line of my previous post said......the 1.4 and optional 1.83 numbers........should read the 1.64, not the 1.4.

On buying props, unless you rock the boat with new data conflicting what's on the table, I think this problem is solved. I think we know where we are and what it will take to get where you want to be. Looks like the Fix is $115 and considering some of the $$$ you mentioned I think you are getting off with a bargain.

Your current 19P 3 blade prop referenced in your communications, running 6400 with no trim (now I know that means no + or - trim, just that the engine is perpendicular to the hull) should load up fine, bringing your rpms down into the recommended range, when you are out on a hunting trip and I would use that prop for that outing.

When you want to play, then right now I'm sitting on the 21P Hustler I mentioned as my choice and I think it will dial in perfectly for you. I don't think you can beat that prop for what it is and for $115 with shipping paid. I have one and know it works. Best I can tell, that prop on the bigfoot prop shaft will need the 501 hub Kit.

If you choose to go that route, get on Live Chat if they have it or call them and determine what I said about the hub part number and use the reference 2.33 gearbox like is on the 90 hp conventional or if their reference is to your 2001 and up 60hp 4 stroke Bigfoot then use that. What you need to ensure is that you verify what "thrust washer" goes with the hub selected and is it in the kit box or does it come separately, as the length of different props are different, especially between rubber pressed in and plastic replacement types and you don't want the prop rubbing on the gear housing nor do you want it sticking too far back where you can't get the nut and washers on with some thread left over. I'm sure that you know that the thrust washer will be tapered like your current one and if you need to use an alternate with your new prop ensure that you match the taper of the washer to the taper of the prop shaft.

Finally, once you change props, obviously things will change. Personally I'd expect your rpms to drop down to around 5500-6000 and your speed to pick up several mph due to the higher pitch which, when considering it will load up the engine from where it is now, lowering rpms, the fact that you can trim back out where you are currently running 7200 and not blow out, or if it does it'll take more trim to make it happen, preventing the high rpm reading and with the extra bite and rpms with less boat in the water (drag) you may get fairly close to your 50 dream.

I just did a www on that engine's recommended rpm range and at WOT it's 5500 to 6000.....perfect! I ran a quick prop slip check and with the 21 Hustler and sweet spot trim, at 6000 looks like 54/48.....-2rpm/50 = - 4%..... that's pretty close to your aspirations especially for what it cost you. Heck, with the cupping and all your slip should improve and -4% of 12% is -.48 for a slip of 11.52 rather than 12 which is absolutely realizable......so you might get your 50 after all. Grin!


Edit. I typed this before I got your last reply verifying the 2.33 and wiring of the tach.

Will wait for your boating trip results this afternoon.

 

[Wood Slayer]

Well the saga will continue! Unfortunately the data was less then impressive.
19p prop 38.5mph at 5450 rpm.
I went threw the instructions given by tiny tach for my setup.
--------
Now playing on go fast BAM.
My 2.33 L/U with 19p at 5450 gave me in theory 42mph, very close.
So when I put in
1.83 L/U with a 19p at 5850, shows in theory 59mph i believe.
Now this that said, im at a cross road. Do you think with a lower diameter prop at 19p and with the new L/U, that I could push 5850?
Thanks for staying tuned!
Rich
Pics coming

 

[Wood Slayer]

[No message]

 

[Texasmark]

Well the saga will continue! Unfortunately the data was less then impressive.
19p prop 38.5mph at 5450 rpm.
I went threw the instructions given by tiny tach for my setup.
--------
Now playing on go fast BAM.
My 2.33 L/U with 19p at 5450 gave me in theory 42mph, very close.
So when I put in
1.83 L/U with a 19p at 5850, shows in theory 59mph i believe.
Now this that said, im at a cross road. Do you think with a lower diameter prop at 19p and with the new L/U, that I could push 5850?
Thanks for staying tuned!
Rich
Pics coming

Ok. Taking your numbers with the 2.33/19 and BAM I find that your slip is only 10% (not my close guess of 12) and your wake affirms that. You have very little hull in the water making the wake flat, indicating minimal hull to water contact resistance, the wake convergence is well aft to the boat meaning your speed numbers seem realistic, and your spray is fine mist

So all your data makes sense and appears to be accurate. Everything fits; sorry too for the bad news, but accurate data is just that.....you have to live with the numbers if real.
---------------------------------------

This changes the whole ball game. What initially appeared to be an excess of HP for your boat now appears to be a deficiency. The recommended rpm range for that engine is 5500 to 6000. You are currently below that range which is classified as lugging. 4 strokers can take it better than 2, but lugging just wears engine bearings and on carbureted engines wastes fuel....On injected engines, the computer may tell the injector to squirt more fuel sensing a lugging condition....dunno.

Your boat, with you alone is a light load even though most of the weight is at the stern and that impacts the hole shot......as you know. Reducing the diameter of your prop is the wrong way to go for that, unless you have something like ports in the prop or a "Whales Tail" to assist in overcoming the stern heavy condition. However a Tail gets in the way at the WOT go as fast as you can times.

It's hard for me to attempt to give you a hard number when switching between the two lower units and really the only way you really know is to test the setup on the boat in the water under operational conditions.

First question, were you alone in the boat today, or were there 2 of you? Anything but basic necessities?

If you were alone with minimal gear then I'd say you are at the top of your performance curve with what you have. 60 hp will only do so much. For hunting trips you owe it to your engine to cut what pitch you currently have to get your rpms up in the recommended region, preferably near the top which has proven to me to provide the best overall performance, fuel economy, and longevity of your engine. On light load conditions, you are just squeaking by.

Switching to a smaller diameter prop running slightly faster will not make up for the 59% reduction is surface area the 10" prop would yield over the 13 meaning that the thrust difference between the two cannot be made up by available engine rpm I think your hole shots would be a dog, especially with a hunting load.

Thrust comes from the prop and propels the boat (obviously). The engine RPMs spins the prop. HP has to drive both and is (Thrust in ft-lbs x prop shaft RPMs)/5252. If thrust goes down, rpms have to go up to maintain the thrust pushing against the water propelling the boat. If the thrust goes down 59% due to a diameter change, your engine cannot rev high enough to increase by 59%. You are on the loosing end of the stick there.

So, rather than dial up pitch as we initially thought would be the case, I think dialing down pitch is more in order and that's done, assuming everything else is constant, 150-200 rpm increase per inch of pitch reduction. Dropping to a 17 from where you are would put your rpms in the ball park and should suit you handily with your hunting load. You can run the numbers but yes it probably will drop your hunting WOT mph but it will improve your hole shot....small consolation?????

One question puzzling me. On your outing today, did you trim out till you blew out? Did you take your data at the 0 trim position.....I think so as that 38 mph speed is where your initial data point at 0 trim was taken as I recall.

Chew on this and come back.

Mark

 

[Texasmark]

In looking for the relationship between diameter and thrust I found an equation for thrust efficiency for Ship propellers on the www. The elements of the equation are:

Shaft thrust, 1st order
water density, 1st order
shaft rpm is 2nd order (squared)
diameter is 4th, (exp 4)


What this does for me is it attempts to reaffirm my feelings about your thrust differences between the 10" and 13" props. The diameters are related by the 4th power.....dxdxdxd. Whopping big number so with a 3" difference in diameter, the change in performance would be like (13x13x13x13) - (10x10x10x10) in thrust efficiency.

Let me put it another way. Back in the 1960's OMC came out with a V4 75 hp that had a 10" prop turned by a high gear ratio like a 1.5 gearbox....small prop turning fast. In the late 60's they came out with their loop charged triple cylinder of 55 hp with a high gear ratio, like 2.3 swinging a (slow turning) 13" prop. When the redesign got to the larger V4 engines (I had a 1972 125 Johnson V4 back then) they too ran high gear ratios and (slow turning) 13" props. The obvious difference was apparent when you wanted to deep water start a pair of slalom skiers. The 13 popped them up and the 10 grunted.

Aside from the dollars you wouldn't have to spend, I think you would do better keeping your current lower unit. The numbers D2-LE2-1319 stamped on the side of your current prop searches out to belong to the LE2 series of Hustler props. I'd go after a D2-LE2-1317 for your hunting trips.

Thoughts?

 

[Wood Slayer]

Mark,
This data is on a full trim blow out! All data is by myself with a light fishing load, minimal tackle. The data is just that! I cant change anything but the setup!
When i was out earlier this week, the river was 3' higher with the current in my favor. I would have never thought it would make a 5mph difference.

So ive come to three choices:
1: we now know a 17p prop with my current setup is what I need. I believe that if i get the prop you suggested (turning point) that i would not loose much top end. I also have a spare 15p prop for my 60 days of waterfowl.

2nd. I can go for a 1.64 or 1.83 L/U and run through a new prop selection. I believe this option would not be optimal for a heavy waterfowl load. But could still work fine as long as I pitch down.

3rd: Repower the rig, I really dont want to do that! But in a end result. The 4 stroke does weight almost 100lbs more then the 2 stroke. And for the weight differences, i could probably move up to a 75hp!

Cost difference which is always a factor.
1: Just a new prop $115 delivered
2nd: $1700 L/U with 2 new props of $230. Lets say $2k total.
I believe I could run in the mid 40's by trying different L/U's and props.
I know I could get a reimbursement of $7-800 with selling my 2.33 and anoth $150-200 for that spare powertech. So lets say $1100 out of pocket for the additional MPH. Hmmm!
3. I dont feel that I would lose much at all, if any. I have a total of $2800 out of pocket right now for my motor setup (not counting tiller handle) Im pretty sure I can sell it in the $3500 range with out the handle. The motor had 210hrs on it and Ive put around 2-4 hrs on it.

Conclusion:
My first move is to go and buy the 17p for $115. I will do this tonight. This will buy me time to stay on the market for a lower unit. I'm also going to do my full research and see what all L/U are compatible with my motor! I would really like to find a 1.83, but would be open to a 1.64 if it fits. Then run through a prop fitting at that point. If I find a used L/U I wont lose any $ but for the props.

If the L/U exchange dosent get me to the mid 40's or low 50ish then it will be a end result in a motor swap.

Mark,
Thank you for your time and expertise! It does not go unrecognized! Im ordering that prop as well as trying to dig up a new used L/U. I may be able to post back next week if i do infact find a L/U.
Richard

 

[Wood Slayer]

Mark,
Last question:
Would it be worth running a smaller diameter prop with my 2.33? I would lose a little hole shot, but can run a higher pitch, lets say a 21 maybe?

 

[Texasmark]

Prop design, as I see it incorporates a lot of variables. I was on the www last night after getting your report, looking for something I could offer you in the way of a formula for thrust in comparing a small diameter high speed prop vs a large diameter slow speed prop and the calculations are complicated and involve many factors...like water density for one.

That really funnels down to when I was young, the guys that raced the little 3 pt. hydroplanes with the Quicksilver (Mercury) lower units ran like a 1:1 direct drive lower unit with something like a 7" diameter prop with something like a 20" pitch on a 40 hp engine. To get them going they would squirt the throttle because the prop had no thrust capability but plenty of hp to spin the prop for the hole shot requirement so they would squirt, blow out, squirt, blow out, etc, and as they repeated the process the boat would gain momentum and once on plane, the little prop would bite and hold and the boat took off.

Flip side was the tug boats I worked on during the last 2 summers in high school had something like a 10' diameter prop with a 1' pitch turning in the low hundreds of rpms but it would push 300,000# of cargo at 10 mph.

When OMC did their new engine I mentioned earlier they apparently realized that the small, fast turning prop, wasn't the answer to "today's" boating requirements and went with what we now have. The other thing may have been that in the redesign of the mid range engines (40-70) when Mercury went from cross flow (Classic Merc 4 cyl) fuel charging to Loop Charging (increased fuel efficiency) which at the time required 3 cylinders to get the exhaust tuning to work with the loop, and in the process dropped the weight and cost of the 4th cylinder and improved performance over the 2 cylinder, they chose to go with the small diameter, fast turning prop possibly purely for weight reduction reasons attempting to win market share with the "lightest" engine in the class. I don't know.

If you look at anybody's conventional (no Cleavers and such) prop lineup you will find that the higher the pitch, the smaller diameter. This has to do with what I mentioned above about the equations that are used in prop design. When we (every piece of information I have ever obtained from reference material and verbally) talk about prop performance, the number that is always predominant is the pitch, not the diameter and maybe that's because the pitch apparently sets the diameter by design.

If you select a shallower pitch in the 13", or any other group, you will find that the trend is that the diameter will automatically grow. If you arbitrarily want to change the diameter of a prop without much of a pitch change then you usually have to get a different style, like a zero rake vs high rake for example. Somewhere in the prop section obtained within the "Boat Parts and Accessories" at the top of the page is a tutorial on props and it explains a lot that may be of interest to you.

Back when I had my 1972 125 Johnson, I had it on an 18' Caravelle tri-hull. I had a shallower pitch prop than I could have run because I had 4 kids and we went skiing frequently and I needed the extra thrust/rpm the shallow pitch gave me for the hole shot with skis. I clearly remember that I could not get from 39 mph to touch the 40 on the speedo which I really wanted, but not at the expense of buying another SS prop.

With that said, my boating associates at the time were running OMC 60 and 65 hp, 15-16' light weight fiberglass (500-600#) boats not necessarily propped for skiing....just ran what came with the rig. We didn't have tachs back then and most of us were naive about the mechanics of boating and fixing problems and all that. We just ran with what we could afford and hoped for something that worked for us. The point here is that none of them could keep up with me nor pass me at 39 mph......aka 60 hp can only do so much.

Your wake shows that you are getting super performance out of your rig with your 60 hp. Personally I was surprised at your aspiration for 50+ on that boat with that engine, but who knows till you try it.....right?
--------------------------
I hope I have answered your question but if you want to pursue a smaller diameter prop fine. I suggested to you where I think you need to go. I said this earlier and only suggested getting a 17P for hunting and keeping your 19 for your fun outings.

With your 5450 rpm I am assuming that data point you took yesterday was at the zero trim position as the speed was 38, not 42 where you were previously blowing out. Now that you seem to have accurate RPM data, you can still trim her out watching your RPMs and get on up to your 42 area within your rated 6000 rpm or a tad above maybe with your current prop.

Then buy the 17P I mentioned and use that for duck hunting keeping an eye on RPMs when running that prop when lightly loaded.

I really believe this is the best route for you from a performance standpoint. With much less emphasis, considering what you have mentioned as possible alternatives, gets you where you NEED to be for a lot less money.

I've been where you are with my boats....never satisfied, if I could just tweak this or that, I could get this or that. It goes on and on. No matter your level, you are never satisfied and seek what you don't have......I've been doing it for over 50 years and had probably 15 or so different boats in the process and with every one, I had the same philosophy..........what if I?????????????????

Want more, ask,
Mark

 

[Wood Slayer]

Mark,
Thank you for all the help and information that you have given over that past three days.
Ive made my final decision of just going with the new hustler prop and staying with the 2.33.
My overall reason for this rig is to hunt waterfowl. I feel that the 2.33 L/U will give me everything that I need and do great in the environment that she will be ran.
Heavy loads, stump fields, big seas and rough weather. I do know that I do not to be in a situation where I need to get on plane in freezing weather and not be able to!
You have nailed it on the head the whole time and especially with your closing statement. "You will always wonder what if!"
-----
If in fact I do chose to go with a 1.83 L/U, you will see me back on here with a whole new set of questions. But, I do know that I will not be selling my 2.33!
Thanks again and best regards!
Richard Capwell
P.S- check out the video from yesterday while trying to collect my data!

 

[Texasmark]

Mark,
This data is on a full trim blow out! All data is by myself with a light fishing load, minimal tackle. The data is just that! I cant change anything but the setup!
When i was out earlier this week, the river was 3' higher with the current in my favor. I would have never thought it would make a 5mph difference.
----------
Reply:

Current vs GPS is addition and subtraction however you are dealing with it as the prop/LU sees it and as it affects the hull drag. Might be a 1:1, might not...going with 5 mph current gain 5 GPS and the reverse loose 5 from a dormant water condition.
------------
So ive come to three choices:
1: we now know a 17p prop with my current setup is what I need. I believe that if i get the prop you suggested (turning point) that i would not loose much top end. I also have a spare 15p prop for my 60 days of waterfowl.
-------------------------
Reply:

So you are thinking about ditching your current 19P and going with a 17? If you are going to do that, then go with the Hustler, but a different prop than your current series which doesn't appear to have porting and cupping. I recommend the iboats Hustler part number: 21431711 with mating hub # 501, $115 and Free UPS shipping. Call and ask if that prop needs a special thrust washer (if the prop length is different from OEM) and if so, is it in the 501 kit. 1. it should give you a stellar hole shot. 2. it will act like an 18P which should put you right at 6k when at max usable trim because the cupping will significantly reduce blow out and if nothing else, will delay when (in the trim angle) it occurs allowing you to go faster.

The 15 for hunting sounds like a great idea. Just watch your rpms when lightly loaded and you should do great.

------------------------------
2nd. I can go for a 1.64 or 1.83 L/U and run through a new prop selection. I believe this option would not be optimal for a heavy waterfowl load. But could still work fine as long as I pitch down.
-------------------------
Reply:

Okaye fine. See if you can get a prop with it and that will give you a starter prop for determining how things are going to work for you and help in determining where you go from there on prop selection. Be sure and get a 20" midsection.
--------------------------------------

3rd: Repower the rig, I really dont want to do that! But in a end result. The 4 stroke does weight almost 100lbs more then the 2 stroke. And for the weight differences, i could probably move up to a 75hp!
---------------------
Reply:

Yes and you would have some props to try with the 75 if you stay with Merc......spline count is the reason which could be changed if you buy another brand for about $35 each.
---------------------------------------
Cost difference which is always a factor.
1: Just a new prop $115 delivered
2nd: $1700 L/U with 2 new props of $230. Lets say $2k total.
I believe I could run in the mid 40's by trying different L/U's and props.
I know I could get a reimbursement of $7-800 with selling my 2.33 and anoth $150-200 for that spare powertech. So lets say $1100 out of pocket for the additional MPH. Hmmm!
3. I dont feel that I would lose much at all, if any. I have a total of $2800 out of pocket right now for my motor setup (not counting tiller handle) Im pretty sure I can sell it in the $3500 range with out the handle. The motor had 210hrs on it and Ive put around 2-4 hrs on it.

Conclusion:
My first move is to go and buy the 17p for $115. I will do this tonight. This will buy me time to stay on the market for a lower unit. I'm also going to do my full research and see what all L/U are compatible with my motor! I would really like to find a 1.83, but would be open to a 1.64 if it fits. Then run through a prop fitting at that point. If I find a used L/U I wont lose any $ but for the props.
-------------------
Reply:

While you are looking over what combination looks right for you, keep your BAM prop slip calculator handy and use 10% for your slip number. You can solve for any box (parameter) you leave blank if the others are filled in. If you put prop pitch in the calculator, ensure that you can purchase that pitch in a diameter that will fit that lower unit which should be in the iboats listings for the conventional lower unit for your 60.
---------------------------------
If the L/U exchange dosent get me to the mid 40's or low 50ish then it will be a end result in a motor swap.

Mark,
Thank you for your time and expertise! It does not go unrecognized! Im ordering that prop as well as trying to dig up a new used L/U. I may be able to post back next week if i do infact find a L/U.
Richard

Sounds like a plan. Gotta know where you're going if you expect to get there. Grin

Stay connected, obviously I am interested on how things are doing/went.

Balls in your court.

Mark