Prop to help push bow down.

[Don Peacock]

First the info:

2000 Lund Gran Baron 2150
Mercruiser 5.7L 250hp Alpha one

Current prop: 3 blade aluminum 14.25 / 19P

WOT is about 5100rpm (which is 250-300 over spec).

Max speed (gps) 52mph with medium load, 20gal fuel etc.

I use the 15hp Merc kicker most of the time (trolling for Salmon, Steelhead, Walleye etc.).

On flat to 2' chop, the boat is fine, but once the rollers really start going, I'm unable to push the bow down enough and end up hitting all the waves with the bottom of the boat. I'm not looking to break any speed records, I just want to push the bow down a bit more, 25-30mph with the bow down a couple more degrees would make the boat perfect.

I've looked at trim tabs, but I'd need a jack plate to set the trolling motor back if I were to install trim tabs. Not to mention the issues with transducer location on an aluminum boat, trim tabs would make it even worse.

So, I've been doing a bit of reading about props and have an idea. If I repropped with a 4 blade SS (stiletto 14.25x20P or 14.25x19P) I'd lower my rpm WOT a bit, and get more 'bite' that might let me push the bow down a bit more, wouldn't it?

Looking for some ideas/thoughts.

A couple years ago, I had a 14.25x19P with cupping and it dropped the rpm a bit and seemed to handle a little better. Unfortunately, I hit a stick and took a chunk out of the prop. When it was repaired, it didn't perform nearly as well.

Other info:
This boat has an 80gal fuel tank and when it's full, I am tail heavy. I think the 4 blade will help lift the boat a bit as well on those rare occasions that I have a co-signer with me at the gas station ;-).

Thanks in advance for your thoughts,

Don

 

[hwsiii]

Re: Prop to help push bow down.

Don,

A couple years ago, I had a 14.25x19P with cupping and it dropped the rpm a bit and seemed to handle a little better. Unfortunately, I hit a stick and took a chunk out of the prop. When it was repaired, it didn't perform nearly as well.

I can almost bet they either used the wrong pitch block or they took the cup out of the prop.

Buy a Solas Amita or Rubex 4 blade aluminum prop and you will lose about 250 RPM and raise the stern which will lower the bow lift and let you break the waves with the vee.

You can try a stiletto but I believe with the high rake design you will still have the bow high problem. If you want a SS prop go with the Baypro II, NOT a Baypro III, and you will be happy as well.



H

 

[robjen1019]

Re: Prop to help push bow down.

agree with Solas Amita or Rubex 4 blade, I put on on my 20ft cuddy and it really made a difference in bow raise.

 

[Don Peacock]

Re: Prop to help push bow down.

Thanks guys,

The Stiletto BayPro II was the prop I was looking at. I'll probably do some serious testing as soon as I get a nice weekend (no rain/wind).

Thanks,
Don

 

[hwsiii]

Re: Prop to help push bow down.

Sorry Don, I was just talking to someone about the Advantage series. LOL



H

 

[Don Peacock]

Re: Prop to help push bow down.

Update, my memory wasn't horrible, but it wasn't perfect either.

I took the boat out yesterday and the rpm is 4950 and the speed was 47-48 depending on the direction I was running across the lake (1' chop and 15-20mph winds).


The WOT range for my engine is 4400-4800, If I go with the Bay Pro II, would you go with a 20 pitch or 19 pitch? I'd be moving from 3 blade un-cupped aluminum to the 4 blade SS Bay Pro II.

Thanks,
Don

 

[ClassyGlassy]

Re: Prop to help push bow down.

What pitch gave you that rpm? If it's the 19 then go up to 21, to get your bow down adjust your trim pin down.

 

[Don Peacock]

Re: Prop to help push bow down.

I had the pitch right, it's 19.

It's a Mercruiser and I can't tuck it in any further.

Don

 

[ClassyGlassy]

Re: Prop to help push bow down.

you may need to look at a whale tail/stabilizer..........

 

[ClassyGlassy]

Re: Prop to help push bow down.

Hydrofoil.....that's what I was saying

 

[Don Peacock]

Re: Prop to help push bow down.

Hydrofoil.....that's what I was saying

Nah, I think I just need a good stern lifting prop.

Thanks,
Don

 

[ClassyGlassy]

Re: Prop to help push bow down.

a "good stern lifting prop" is ONLY going to work until you are on plane, then it's going to cause you to run an even HIGHER RPM which will hurt your motor if you're not watching it! You already stated that your current RPM at WOT was more than what's rated.......with the 19p prop and you'll have to go down to a 17p prop to give you more hole shot to get up onto plane.

You stated that at near glass water with up to a 2" wake you can get it to plane just fine.......your problem shows up in choppy water. You need to look into a wedge then to get your drive into the right relationship with the boat since your trim isn't working.......

Prop at your own risk.................then start looking at what REALLY is making your boat not want to plane.

 

[hwsiii]

Re: Prop to help push bow down.

Don, try reading this, then get back with me, and I need to know what your lower gear ratio is as well. And let me know how many people you normally have on the boat, and how many you had with you this last test.

You might try reading this for a better understanding of changing props for better performance, and for the major differences between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057




H

 

[Don Peacock]

Re: Prop to help push bow down.

I think you are thinking of a different post. I have zero problem getting on plane. My issue is getting the bow down into 2-3' rollers while on a slow plain (20mph or so). I can stay on plane, but I can't 'cut' the waves with the V.

a "good stern lifting prop" is ONLY going to work until you are on plane, then it's going to cause you to run an even HIGHER RPM which will hurt your motor if you're not watching it! You already stated that your current RPM at WOT was more than what's rated.......with the 19p prop and you'll have to go down to a 17p prop to give you more hole shot to get up onto plane.

You stated that at near glass water with up to a 2" wake you can get it to plane just fine.......your problem shows up in choppy water. You need to look into a wedge then to get your drive into the right relationship with the boat since your trim isn't working.......

Prop at your own risk.................then start looking at what REALLY is making your boat not want to plane.

 

[ClassyGlassy]

Re: Prop to help push bow down.

I think you are thinking of a different post. I have zero problem getting on plane. My issue is getting the bow down into 2-3' rollers while on a slow plain (20mph or so). I can stay on plane, but I can't 'cut' the waves with the V.

that just confused me even more!

Then you need to just look into power trim...................

And you need to Pitch UP to get your RPM down to the proper range!

 

[Don Peacock]

Re: Prop to help push bow down.

Thanks for the link, it was a very good read. I believe my gear ratio is 1.47 (2000 merc Alpha).

I calculated my prop slip according to the link at 21.76%. (4950rpm, 47.4mph, 1.47gear ratio, 19p prop)
I ran the lake 4 times with and against the wind. My actual top speed average was 47.4mph.

As I mentioned before, I had a 19p with cupping that always performed better than my current 'rebuilt' prop.

After reading the article, I'd expect to drop around 200 rpm going from my current 3 blade 19 to a cupped 4 blade SS at the same pitch. That would put me at 4750 WOT which is perfect. My load was probably 300lbs lighter than my typical load. It was just me and my fishing buddy, but we didn't have any of our tackle or the fish cooler on board, Frankly I don't notice much performance difference until I start adding 1000lbs or so (3 extra guys + their stuff + my tackle) above what I had yesterday.

I'm not settled on any particular prop yet. I really appreciate all the input here, helping me understand the trade-offs and the 'likely' affects of the change.

Thanks,

Don

Don, try reading this, then get back with me, and I need to know what your lower gear ratio is as well. And let me know how many people you normally have on the boat, and how many you had with you this last test.

You might try reading this for a better understanding of changing props for better performance, and for the major differences between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057




H

 

[hwsiii]

Re: Prop to help push bow down.

Don, if you buy the Baypro II in a 20" pitch I expect your speed to go to about 50 MPH and your RPM to drop to about 4,600. You should be able to buy one on IBoats for about $ 240.




H

 

[Don Peacock]

Re: Prop to help push bow down.

Thanks,

I will keep waiting for a sale and if it drops to $240, I'll order one.

Thanks again,
Don

Don, if you buy the Baypro II in a 20" pitch I expect your speed to go to about 50 MPH and your RPM to drop to about 4,600. You should be able to buy one on IBoats for about $ 240.




H

 

[gss036]

Re: Prop to help push bow down.

I would suggest Bennett Trim tabs, then you can make the adjustments you need, I don't think the 4 blade prop will be the answer to cutting the chop. I went to the 4 blade and raised my engine to stop porpoising because of the heavy weight of the Honda. I am running a 225 Honda outboard w/a power tech 4 blade stern lifting prop and still use my trim tabs in chop. It is just a necessary evil to have in choppy waters. I run a Yamaha T9.9 long shaft. Previous kicker was a 15 hp Honda.

 

[hwsiii]

Re: Prop to help push bow down.

Don. it seems Iboats is out of them, but the only ones I an find for $ 240 fit yamahas.

http://www.gandermountain.com/modperl/product/details.cgi?i=27219



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