Hwsii prop recomendations for a Whaler

[Tig]

I'll apologize up front for this being long winded but I spent a year thinking this through, setting up the boat and testing. I hope I got it right. If I missed something, please let me know and I will get the information you need.

I have had my own motor boat since I was eight and I have owned this particular boat for one year. Last season was a very short one for me due to work, so I'm still feeling it out. When I first got this boat, a stainless prop was at the top of my shopping list. I pretty much knew exactly what I was going to buy. Then I started reading the Iboats prop forums and the Hwsii white papers. Over time I came to realize that the prop I wanted is not the prop I need.

The boat came with an aluminum elephant ear prop I believe it's a 13" pitch but it has no markings. I ran it for a week or so then I swapped in the spare. The spare was a 11 1/4 x 13, 3 aluminum prop I believe it's what's called a semi cleaver. I tested both for the heck of it. Too bad about the one being unmarked.
Last year the anti-vent plate was 7/8" below the keel and I ran 33.7 mph on the GPS with two adults on board at 6300 RPM. (tail wind) This spring I raised the motor up two holes all the way to the top. The anti-vent plate is now 5/8" above the keel.

The boat will porpoise very easily if both occupants are at the helm. Loaded this way she does not like much trim, only two touches up with the semi cleaver, one touch with the elephant ear. Next tap and she starts to porpoise. That being said, it's an open boat with room for 4 in the bow. Last year on one occasion I had a capacity load (over 850lbs) with over 500 lbs of it in the bow. It did not plane until I trimmed the motor up two taps, which I found odd. Once on plane the boat trimmed out beautifully and ran as if it was meant to carry that load, in that way.

It's windy here and white caps are part of a nice day on the water. Under normal load when the waves get to two feet the ride suffers with a light bow.

Getting good numbers is quite an interesting process as I found out.
First WOT test after raising the motor. Average load, two adults. 32.8 mph @ 6500 rpm. ~14% slip I was trimmed up and it must have been ventilating a bit. I had never seen it run 6500 rpm before. I don't consider this a "good" number since it is not reproducible.
I also tried a solo run against the wind in a light chop @ barely 6000 rpm I hit 33.9 mph. ~6% slip, but this is not a typical load.

Now the real numbers;

1. Boat:
1995, Boston Whaler Dauntless 15, 9 degree deadrise at the transom,
Max rated hp 70 on the plate (60 in the original manufacturer brochure that I found in online archives)
15'1" L, 6'4" wide, 850 lbs base weight

3. Normal use and load:
Cruise and fish, normally two people, both sitting at the helm when under way. 6 gallons of fuel. Total running weight estimate ~1550 lbs
This boat does see stretches of Lake Ontario where agility is valuable for a smaller vessel. Day trips require crossing a 5 mile stretch where 4' seas are common in the afternoon.
Occasional ski/wakeboard and max capacity cruise in sheltered waters.
Local elevation is about 250'

4. Engine:
Honda, BF50A, 1995, 50hp, Gear ratio 2.08, RPM range 5500 to 6000 RPM, weight 208 LBS

6. Anti-ventilation Plate height above keel of boat.
5/8" above keel. Recently raised engine to the bottom hole on the engine bracket. This is as high as she will go.
Click to enlarge pic.


7&8. Props and performance specs with typical load of ~1500 lbs:
Aluminum prop, unknown manufacturer.
11 1/4 x 13 semi cleaver
RPM GPS mph
4000 17
4500 22.1
5000 24.6
5500 27.8
6000 31
WOT ~6050 31 mph

Prop has pits but no dings. It appears to have been repaired at one time.
No trim tabs, whale tails or other goo gahs on the hull.



Second prop.
Elephant ear prop with absolutely no markings other than an R. I include this data for the purpose of illustrating the different loads that it was tested under.
Passenger in bow. I Was able to trim to 90 degrees before it ventilated.
RPM GPS mph
4000 12
4500 18.5
5000 22.8
5500 26.1
6000 29.2
wot ~6050 29.6 mph

Passenger with me at the helm.
RPM GPS mph
4000 15.3
4500 20.6
5000 23.4
5500 26.8
6000 29.2
wot~6100 30.2
Observations: Tolerated less trim than the semi cleaver, one touch only.
Hole shot did not feel as good, (impression)



Here is a pic of the anti vent plate at WOT with a typical load, which is two people sitting at the helm.



Based on that pic it may seem that the motor could go up one more hole, but there isn't another hole.
Here is a pic of the trim angle of the motor while running with two at the helm. Note the angle of the anti-vent plate to the keel.



Below is a pic of the anti-vent plate at WOT if a passenger rides in the bow. I guess a small open boat with moderate power is all about weight distribution.



9. To prepare the engine I decarb'd it with seafoam. Seemed to be pretty clean.
Checked and adjusted the idle air mixture. It ran best set to manufacturer spec.
Sync'd the the carbs.
Oil is fresh. Plugs are clean and gaped to spec. Compression was tested last year.

10. Performance issue I am trying to correct;
This boat spends most of it's life around 25 mph with two people sitting at the helm. Currently I have 18% slip at that speed.
Top end is good, mileage is good, hole shot is OK. At capacity it's not much of a hole "shot", but we plane.
I would like to go to an SS prop in search of marginal performance gains. If I could choose where any gain went it would be to hole shot. I can't afford to loose performance there.

Thank you very much for taking the time to recommend a prop for me.

 

[steelespike]

Re: Hwsii prop recomendations for a Whaler

You did a very good job.Hopefully H will be along with some reccomendations.
He favors the Solas amita 4 blade props with some very good results.
I think it would be a good match.You appear to need low to mid range improvements.It should improve your hole shot,resist venting,stay on plane with less power,and offer better low speed control.
You might consider more height with the 4 blade.

 

[Tig]

Re: Hwsii prop recomendations for a Whaler

Thanks Steel. I have read a lot of what you guys have written about the Solas amita 4 blade props. They do sound like a good prop.
Two more holes up would be nice to work with but I've run out of room on the transom when it comes to raising the motor.

 

[hwsiii]

Re: Hwsii prop recomendations for a Whaler

Steve, I will need to spend some time reading and digesting everything that you have written about your setup. BUT you have done an excellent job of giving me all of the information needed, I will get back with you tomorrow night with my analysis.

But, right off the bat I question why you are running such negative trim, unless you are trying to stop the boat from porpoising, because you shouldn't be getting maximum RPM and speed at that trim position.

Here is a pic of the trim angle of the motor while running with two at the helm. Note the angle of the anti-vent plate to the keel.

H

 

[Tig]

Re: Hwsii prop recomendations for a Whaler

But, right off the bat I question why you are running such negative trim, unless you are trying to stop the boat from porpoising, because you shouldn't be getting maximum RPM and speed at that trim position.

H

Thanks H
And yes you are correct, porpoising limits trim angle when I have a light load.
When I consider that the load capacity of the boat is greater than the hull weight, porpoising with my "average load", does not surprised me since seating arrangements dictate that at capacity, 4 of the 6 occupants will be in front of the helm. Arranging the "average load" in a more balanced manner probably won't happen since the Admiral prefers to sit at the helm, where she can keep an eye on the captain.
During the second prop test I did experiment with load balancing. I was able to apply positive trim and ventilation was the limiting factor. Performance seemed to be less at lower rpm. At WOT the numbers were pretty close. It's the first time I ever watched tach and speed with a load like that, so I can't say if the results are typical.
For what I do, I'm demanding a lot of versatility from my 15', 50 hp rig and I am pleased with it's capability.
If it would be helpful I could put the marked prop back on and do another set of tests with different load arrangements. Perhaps I can find a performance sweet spot.

 

[hwsiii]

Re: Hwsii prop recomendations for a Whaler

Steve, I am working on your setup right now and will have some comments in the next couple of hours, my thoughts at this stage are that we don't want to change props yet, we need to look at the overall picture. And I think we want to go with a set of Smart Tabs first to get rid of most of the porpoising, as I believe your maximum expected speed is about 35 to 37 MPH, with everything perfect and 2 people.



H

 

[hwsiii]

Re: Hwsii prop recomendations for a Whaler

Double Post

 

[hwsiii]

Re: Hwsii prop recomendations for a Whaler

Steve, I will try to go through your post point by point.

The boat will porpoise very easily if both occupants are at the helm. Loaded this way she does not like much trim, only two touches up with the semi cleaver, one touch with the elephant ear. Next tap and she starts to porpoise.

When you have a boat with a bow that is almost as wide and heavy as the transom without the motor it is harder to keep the bow in the air for the least amount of drag, and it makes porpoising very easy for the boat. I own a 16' sundance flats boat that the hull form is almost exactly like yours and I have a 40 HP motor on it and I attain 30 MPH with it. I installed a set of smart tabs on it, I have the motor as high on the transom as it will go and I use a Michigan Wheel SS Apollo 14" pitch prop.

The smart tabs stopped all of my porpoising and with the Apollo prop's rake and blade size I am still able to pick the bow up in the air and therefore reduce my surface drag and it lets me be able to raise the bow as well for different wave conditions.

Last year on one occasion I had a capacity load (over 850lbs) with over 500 lbs of it in the bow. It did not plane until I trimmed the motor up two taps, which I found odd. Once on plane the boat trimmed out beautifully and ran as if it was meant to carry that load, in that way.

That is normal, when you have all of that weight in the bow and you have the prop tucked under, as with the prop in that position it is pushing down on the bow and with all that weight in the the bow the boat has to rise in order to break all of the drag and surface tension to get on plane, and that is why you have to trim the motor up.And theoretically it will raise the stern as well, so the prop is higher in the water column.

That is why the smart tabs will work so well, they will keep the bow down until you apply a good bit of positive trim to the motor to raise the bow, and this will also help you to attain maximum speeds.

6. Anti-ventilation Plate height above keel of boat.
5/8" above keel. Recently raised engine to the bottom hole on the engine bracket. This is as high as she will go.

I wish we could raise the motor higher as that helps to get the maximum speed possible out of the setup.

7&8. Props and performance specs with typical load of ~1500 lbs:
Aluminum prop, unknown manufacturer.
11 1/4 x 13 semi cleaver
RPM GPS mph
4000 17
4500 22.1
5000 24.6
5500 27.8
6000 31
WOT ~6050 31 mph

Prop Slip and Effective Prop Pitch

10. Performance issue I am trying to correct;
This boat spends most of it's life around 25 mph with two people sitting at the helm. Currently I have 18% slip at that speed.
Top end is good, mileage is good, hole shot is OK. At capacity it's not much of a hole "shot", but we plane.
I would like to go to an SS prop in search of marginal performance gains. If I could choose where any gain went it would be to hole shot. I can't afford to loose performance there.

I don't know exactly which prop would be better at this time, but after you install the Smart Tabs SX we will see where we are, they run about $ 100. And at this time, in my opinion, that is best investment you can make.



H

 

[Tig]

Re: Hwsii prop recomendations for a Whaler

Thank you for your reply H. I can see you put a lot of thought into it and I certainly respect that. I understand trim tabs, but I have no interest in putting them on my boat. I would elaborate but I do not want to seem like I am asking you to compromise on the conditions you require to make a prop recommendation.
Thank you again for taking the time to consider my request.

 

[hwsiii]

Re: Hwsii prop recomendations for a Whaler

Steve, I want you to elaborate, it is your boat not mine so it is your choice of what you do and don't want to do.



H

 

[Tig]

Re: Hwsii prop recomendations for a Whaler

Ok H,
We're just getting ready to jump in the boat and visit the in laws. I'll summarize my thoughts later.
I'm just trying to not sound like one of those guys who asks a question and then doesn't like the answer, even though that is essentially what happened.

 

[hwsiii]

Re: Hwsii prop recomendations for a Whaler

No, I don't look at it that way, and I do want to hear your objections and understand your philosophy on the trim tabs.



H

 

[Tig]

Re: Hwsii prop recomendations for a Whaler

Sorry for the delay, I had to collect my thoughts. My philosophy/opinion is based on 40 years of personal and professional experience. It's much broader than just trim tabs so I'm trying to avoid writing a self serving novel.

I'm a lifetime boater and have had my own boat since 8 years old when my brother and I claimed an abandoned boat. We stuck a 3 hp motor on it and tried to make it go fast. As kids the highlights of the season were the new Evinrude catalog and the Gold Cup races. We'd see the sportsman class boats fly down the straight, trimmed and tabbed running on that little patch of Teflon paint. Entering the corner they'd drop the bow just enough to get back to the straight. That's what we wanted to do. We'd walk the pits before and after the races, examining the setups asking about every mod and trick we spotted on the boats. Much later I did have a 60 MPH boat and friend of mine even had a +90 MPH boat.
In 1980 I had a 400cc bike that I modified extensively. I could pull red-line uphill at 120mph. I went on to be involved modifying cars, trucks and even a 9 second drag car where I did some ignition work. One thing I noticed on the way, was that while each mod held promise of performance gain it also had a definite cost in terms of maintenance and often versatility. It was a trade off.
Moving on..... for the past 25 years or so I have made a living maintaining mainframe computers and peripherals. I noticed that competing manufactures would design equivalent machines with very different philosophies. Some so simple it was amazing how well they worked. Others so complex, it was a wonder that it ever worked because there were so many potential points of failure.
Over time I have seen simple machines out perform complex ones. I have come to appreciate the elegance of simple design. I have applied that philosophy to the things I own. I buy a simple machine that suits me and I run it as it was made. I avoid adding unnecessary points of maintenance. Smart tabs are not for me.

So if I review my boat's performance, it looks this way to me;
I chose to power it at 71% (50hp on 70hp max) with a 4 stroke engine which will be a bit heavier than it's 2 stroke counterpart.
It still planes and runs nice with a capacity load.
Can pull red-line at over 30 mph.
Gets more than 10 mpg.
Handles very well across a wide range of water conditions.
None of this is record breaking by any stretch, but it pleases me and compares well, especially if you consider that I run aluminum props.

Now, left to my own devices in picking an SS prop I would consider the following factors;
Poor hole shot is noticeable. Good top end, not so much. Based on capacity load observations, 3800 rpm seems to be the make or break point for hole shot.
Some stern lift would be desirable, since I often run with a light bow in rough water.

Studying the forums and manufacturer sites gives me an idea of what to look for, but at the same time, hard technical specs are not readily available beyond effective pitch and diameter. Even if they were, this is not a simple matter. From what I understand the following characteristics would be desirable in my SS prop. 4 blade, cupped, semi cleaver(ish), easy on the rake. From what I have read, a vented prop does not suit my application. Comments?

4 blade SS on a BF50A seems to narrow my choices to the Powertech line of products. Unless you can direct me to a line I've missed.

I hope some part of this makes sense.

 

[Tig]

Re: Hwsii prop recomendations for a Whaler

I'm going to bump my old thread for the purpose providing feedback on the changes I've made and the results. I hope that's acceptable.
Life got busy and I didn't actually buy a prop until yesterday.
First off, motor mounting with the anti ventilation plate 5/8 above the keel was too high for my low tech aluminum prop. It ventilated easily.

So on goes a Solas Amita 4, 12" pitch. I'm looking for better holeshot with a max load, redline at WOT and 30ish mph.
The change in prop is rather drastic from the semi cleaver, no cup, 3 blade prop. First impression; it's a funny looking thing. More like mouse ear than elephant ear design. Semi cleaver looks way cooler.

I was hoping it would work out as follows. 13" pitch down to 12" (rpm up) and three blade to four (rpm down) would be a trade off. Negligible impact on rpm. Straight blade to cupped blade is hard to estimate the impact of reduced slip, but I was hoping that my occasional 6300+ rpms would be tamed into 6000. I like the revs at the high end of the range because 50hp is on the low side for my boat.

First test run was an evening cruise with typical load.
Hole shot impressions. tach jumps to 4500, where she heels over to plane. Seems good, but that is more of a concern when I have a max load. I won't get to test that for a bit.
Motor height issues are gone. I over trimmed it without a hint of ventilation. I'll credit that improvement to cupped blades.

A few numbers, both directions, cross wind.
RPM ... GPS mph ...... Slip %
5000 .. 26 ........... 4.8
5600 .. 29 ........... 5.2 WOT

Next day solo run, both directions ,cross wind.
Hops on plane very nicely.

RPM ... GPS mph ...... Slip %
4000 .. 18 ........... 17.6
4500 .. 22 ........... 10.5
5000 .. 26 ........... 4.8
5500 .. 29 ........... 3.4
5800 .. 31/32 ........ 2.1@31 mph << Slip seems unrealistically low. RMP was probably a bit higher

When I got back from the solo run I left the engine trim at the WOT setting. Once on the lift I checked with a straight edge and to my surprise the trim is neutral, perpendicular to the keel. I did not expect to find that. From what I understand, low rake contributes to that improvement. Time to recalibrate my trim gauge.

Slip numbers look great. Mid range cruise speed increased. Max speed is within expected range. WOT RPM looks close to where I wanted it. This mouse ear prop seems to work very well. We'll see how this plays out with a max load. Any loss in performance in that area will be painfully obvious.

After thoughts;
I can't help but wonder how a new 3 blade 12 pitch would work. I'll have to see what Pete's prop shop has in stock for SS props. The Solas 4 blade 12 was special order so no exchange privileges. Exchange seems to be the most pragmatic way of dealing with the subtle and not so subtle differences in design and the performance results they bring.
Although the math involved in propeller design is more than I will ever need to know, it would be nice if prop manufacturers would publish more complete technical information on their products. Details on blade shape, thickness surface area, amount of cup, and rake would help you make an informed change even, if only within their product lines.
Lots to consider before I buy an SS prop. Like maybe get one that comes with a 60hp motor.

 

[steelespike]

Re: Hwsii prop recomendations for a Whaler

A nice report.I wish H was around to see it.As we have all discussed at various times the 4 blades forte is low to mid range performance. You may notice slightly smoother operation and a little quicker response at the dock.While yoiu lost a little top end it seems strong.

 

[Tig]

Re: Hwsii prop recomendations for a Whaler

Steele, I do have to thank you and H for your thoughts and all that you have posted in the forums on props.
When I first brought the boat home two years ago I "knew" right away that it needed a 14 - 3 SS prop and I almost bought one. After reading the forums and gathering all the data you guys wanted it became apparent that 14P was not the prop for me. Charting out the rpm, mph and slip really paints a picture. The effective prop pitch number in H's chart is also something to think about. Right now it wouldn't surprise me if a 12 - 3 SS was the best choice for me for general purpose and cruising. But then again, I'm not sure there is much left to gain performance wise other than getting closer to redline.
The admiral and I went to visit her parents last night. It's ten miles each way. I noticed that with two at the helm we seem to be trimmed in a bit from neutral. We were also bliping 31 mph on the GPS when I opened it up, although we were still a few hundred rpm below redline.