Newbie Prop and WOT question

[svkb]

Re: Newbie Prop and WOT question

Ok can't weigh the trailer seperated from the boat. If you can weigh the boat and trailer together and see what ya got.... Just for peace and mind tho...

I take it you store indoors always? This is just me but when i pull my boat i always pull the drain plug to see how much water i am taking on...people getting in and out of the boat wet,splashing and so on... the water has to go somewere, Plus i like to see if i have an unusal amount of water also...ie the bellows leaking or so on....

But i have to store outdoors so i always leave the plug out... rain water!

Others could be on to something with the prop refurbished.. do you have a local marina near by? Sometimes they will rent props for sea trial.

Any Boating friends with spare props?

Good Luck!

My father in law has a 2005 tahoe fish/ski boat with a 4.3 but I don't know what he has for a prop. One of his good friends is a VERY good boat mechanic and I'm currently trying to get in touch with him to see if he can give it a look over. Next time I'm on the highway I'll pull into one of those road side scales and check the weight. I'm guessing the trailer weighs 500 - 600 lbs, but thats just a guess.

It was always indoors from the previous owner and I stored it indoors until my father sold his farm in April, since then it has been outdoors, but has ALWAYS had a completely waterproof boat cover on it.

 

[Philster]

Re: Newbie Prop and WOT question

Old bow riders of generic build quality can take on water at the deck/hull joint and store it in the foam. Number one point of entry for water is the joint (behind rub rail).

When dealing with under-performing old boats, one is required to investigate the weight of the boat for fear of water-logging and to investigate the health of the engine.

svkb: Where do you boat? Curious.

 

[svkb]

Re: Newbie Prop and WOT question

Old bow riders of generic build quality can take on water at the deck/hull joint and store it in the foam. Number one point of entry for water is the joint (behind rub rail).

When dealing with under-performing old boats, one is required to investigate the weight of the boat for fear of water-logging and to investigate the health of the engine.

svkb: Where do you boat? Curious.

I'm from Manitoba Canada, so I hit the variety of lakes in my area.


On a side note, my father in law who knows boats quite well commented that he though it got up on plane pretty quick. Would it still be able to do this if it was really waterlogged?

I'm definitely going to weigh the boat and trailer. Any idea what the trailer would weigh? I know the dry weight of the boat is supposed to be 2,200 lbs.

 

[QC]

Re: Newbie Prop and WOT question

Why in the flying flip are we talking waterlogged? This boat is going FASTER than it is supposed to, not slower :facepalm: This thing is showing negative 22% slip. One number is wrong in our equation. Since we are confident in RPM and Speed (no current right?). Then it has to be pitch or Gear ratio (1.98 in 1991).

We have a newbie here, who is giving us excellent info and we are driving him crazy. His first post indicated that he understood the boat is going to fast for the math, and then we start telling him why it is slow? We need a do over!

Start here:

Yes the boat has a working tach and I compared it to my timing light. The boat tach reads 100 - 150 rpm low. So my WOT confirmed with a timing light is 3900 - 3950 rpm and top speed of 33 -34 mph confirmed by gps. This was my initial question, with a 2.0 drive and (supposedly) a 15" pitch prop, how could I possibly be getting that kind of speed at that rpm? Unless the prop is not really a 15" (even though it's stamped as such) or the gear ratio has changed. I'm going to check the gear ratio tonight hopefully.

It is VERY possible that the prop is no longer a 15p prop. I have seen thousands of so called "repaired" aluminum props that are NO where near there so called pitch number. At this point I would obtain a borrowed KNOWN good prop and rerun your tests. Right now your numbers just aren't adding up correctly

I was wondering that myself, given the fact that I live in the middle of the prairies, we do not have a lot of resources for good boat repair! I questioned the repair last fall when it was done, but it "looked" good.

It would also be virtually impossible to borrow a prop around here, but I'll definitely ask around.

 

[QC]

Re: Newbie Prop and WOT question

I just did a calc that shows a 1.5 ratio drive would give a 8% slip if this is truly a 15 pitch. At least it is the realm of possibility. If the prop has been cupped or modified up to a 16 inch pitch we are 14%. Could be.

 

[svkb]

Re: Newbie Prop and WOT question

I just did a calc that shows a 1.5 ratio drive would give a 8% slip if this is truly a 15 pitch. At least it is the realm of possibility. If the prop has been cupped or modified up to a 16 inch pitch we are 14%. Could be.

Thanks QC I was starting to freak out thinking that I may have a complete dud on my hands. While I will still check into the whole waterlogged scenario to confirm or rule it out, it just wasn't making sense to me. (given the limited boat knowledge that I have) I DO have a very strong mechanical background and after some internet reading, I have a strong understand of pitch and gear ratios and I did the exact same calculation that you did and came up with the same ratio. I just found it unlikely that this boat has had the gears redone, but I suppose it is a possibility. I'll also do a full tune up including timing, filters etc.

Why would anybody regear to a taller gear ratio in a boat with a 3.0 litre engine???

Are the ratio possibilities endless for these units, or is it more like a truck where you tend to stay in certain ranges ie: you see ratios in a truck like 4.10:1 or 3.55:1.

 

[Philster]

Re: Newbie Prop and WOT question

To QC: His engine is failing to turn a 15p prop up to 4600 RPM.

We just ignore that? I buy a two decades old boat, then I'm getting the boat and engine checked.

Yeah, the prop could be a freak and be way off in pitch after a repair. Okay, now there's three things to check. Also, since the prop is a wildcard and the drive ratio is too, even the variables involved suggest that the boat and engine need to be checked.

So, I will revise my order of variables:

Prop... engine... water...

I blew past the prop part. Get a real 15p on there for a baseline. Would love to hear about it.

 

[QC]

Re: Newbie Prop and WOT question

We just ignore that?

I think we do until we get the data right. Your new order of things may be right, but I just don't think we end up at boat issues with a 3.0 at under WOT RPM that planes out OK and goes 34. Probably making less than 110 Horsepower at that RPM. Not too shabby speed for the output

 

[81 Checkmate]

Re: Newbie Prop and WOT question

SVKB - I think your gear ratio is right at 2.0 for a 3.0 motor. Thats what is on my pontoon boat, same set up... never been messed with.

In reguards to someone switching gears... it takes alot of know how and special tools to do that + expensive. Heck You can buy a whole new unit for $1200 bucks. I dont think someone has done anything to it.

Post over in the Mercruiser I/O section on your drive ratio... i am sure Don or Bondo can answer that one.

 

[svkb]

Re: Newbie Prop and WOT question

Ok, if I'm going to look at doing things in the right order, this is what i will do:

1. Confirm what gear ratio I actually have
2. Lift front of boat and let sit for a bit to see if I get any water coming out.
3. Buy the correct prop based on that information (If I do in fact have a 1.5:1 ratio, what pitch prop do I want in theory?)
4. Give the engine a tuneup and ensure I have good gas.


5. Test run

 

[svkb]

Re: Newbie Prop and WOT question

SVKB - I think your gear ratio is right at 2.0 for a 3.0 motor. Thats what is on my pontoon boat, same set up... never been messed with.

In reguards to someone switching gears... it takes alot of know how and special tools to do that + expensive. Heck You can buy a whole new unit for $1200 bucks. I dont think someone has done anything to it.

Post over in the Mercruiser I/O section on your drive ratio... i am sure Don or Bondo can answer that one.

I find it unlikely also, but the speed I'm getting at the rpms would require a 25 pitch prop! The stamp on the prop says 15, it has been repaired, but can it really be out that much??

 

[QC]

Re: Newbie Prop and WOT question

If it's a 1991 it is a 1.98:1 so, yes, effectively 2. It is very easy to switch ratios. You just figured out the easiest way. Swap the unit with another

 

[81 Checkmate]

Re: Newbie Prop and WOT question

I would stick with your plan as you have listed, especially the tune up....... Proly hasn't been done in awhile...
If not water logged... then head back to the lake for testing

Ask around the marina and some boaters for some help with a demo prop... boaten people seam to be a little nicer than one would think

Keep posting results on iboats and these gents will get it narowed down for ya.

Good Luck and Happy Boating

 

[Philster]

Re: Newbie Prop and WOT question

I think we do until we get the data right. Your new order of things may be right, but I just don't think we end up at boat issues with a 3.0 at under WOT RPM that planes out OK and goes 34. Probably making less than 110 Horsepower at that RPM. Not too shabby speed for the output

I admit blowing past the prop part. 2:1 should allow it to spin a 15p. It's pretty rare to dip below that. The prop could be an abomination by now.

 

[QC]

Re: Newbie Prop and WOT question

I find it unlikely also, but the speed I'm getting at the rpms would require a 25 pitch prop! The stamp on the prop says 15, it has been repaired, but can it really be out that much??

I'm getting 20 inch pitch with 10% slip. Using 1.98, 34 and 3950. So we aren't in never never land.

Oh, and just for clarity, Bond-o and Don don't know nuttin'

 

[svkb]

Re: Newbie Prop and WOT question

Wow! You guys are super helpful and so quick to post back! It's AWESOME!! I'm on several other non-boating forums and when you post a question, it's hours, sometimes days before people get back to you. (and more often than not it's some snarky remark!!)

 

[QC]

Re: Newbie Prop and WOT question

Glad we could help. Have you figured out how to check ratio?

Phil and I get snarky, but that's just at each other

 

[svkb]

Re: Newbie Prop and WOT question

Glad we could help. Have you figured out how to check ratio?

Phil and I get snarky, but that's just at each other

Well, I'm not going to pull the lower unit off (did that in winter to change the gimble and check everything over and change oils) so I'll just turn the engine over slowly while in gear... right??

 

[QC]

Re: Newbie Prop and WOT question

Yep. Take the spark plugs out.

BTW, very few "newbies", or oldies for that matter, give us as much good info, and understand as much as you do

 

[svkb]

Re: Newbie Prop and WOT question

Yep. Take the spark plugs out.

BTW, very few "newbies", or oldies for that matter, give us as much good info, and understand as much as you do

Well, thanks for the compliment! As I mentioned earlier I have a lot ot mechanical knowledge ( I was a heavy duty mechanic for a number of years) just no experience with boats! Some things you may not have to explain but others you might have to, so better to assume I know nothing, than to have to explain yourself twice!!