Propeller problem?

kallewell

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Oct 15, 2014
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Hi guys!

I'm new in here, from Norway.
In 2006 I bought a 1996 model 2150 Wellcraft Eclipse with Volvo Penta 5,0 FL with Cobra SX drive. Engine power is 190hp.
Last summer, my engine broke down, and I bought a new one, same engine, just modified to about 305 hp.
Mounted it this season, and was hoping for 50 knop (app 57 mph).
Earlier, with 190hp it went maybe 40 knop.
With my new engine, we have tried different propellers. Different sizes and picth.
The new engine is supposed to run at about 4800rpm.

With my alu propeller 14 1/4x21, my originale propeller in steel 14 1/2,x20, the boat went maybe 42-43 knop.
There was no problem to reach 4800 rpm alone in the boat, or with 5 people. Means that there is more potentiale in the engine and boat.
I borrowed a steel propeller 14 1/2x25. That wass TO heavy. Reached only 4000 rpm, and acceleration was horrible!
Just orderer a new one, steel, 14 1/2x22, haven't got it yet.
But the BIG problem is that the boat seems to not lift itself from the water.
When I'm at 3000 rpm, I can trim the drive, and lift the boat from the water, leaving as little as possible of the boat in the water. That means I will reach higher topspeed. But when at 4000rpm and more, the boat doesn't lift, and you can feel the whole boat beeing in the water. This means it will go slower. When I trim the drive more, it makes a big roostertail instead of lifting the front.

Anybody here that knows anything about this..?

Hoping someone can help me out with this
smile.gif
 

steelespike

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Apr 26, 2002
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Your description seems to indicate a hull problem.If it has trim tabs release them all the way.
The hull may have a hook in the bottom near the transom.Lay a straight edge along either side of the keel. Bottom should be straight.
 

kallewell

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I have no trim tabs on the boat.
I've seen these boats beeing sold with less hp then mine, claiming that the boat reaches over 50 knop..
Hull problem? You mean the whole keel under the boat not is straight..? If so, it should have been in an accident earlier I guess ;)
Visually, it seems to be no problem with the keel. It's still on water, but I'm soon taking the boat on land.
 

Chris1956

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Mar 25, 2004
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A 5.0L motor would normally have about 220HP. Modifying it to make 305HP seems like it would be hard to do. It would be helpful for you to confirm what HP you have.
 

kallewell

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My original engine, delivered with the boat, had 190 hp. This new one is built in USA, with bigger pistons, different camshaft, double valve springs.. I had to change gaspump, cause my earlier didn't deliver enough gas.
It sold as a 305 hp engine, but say it delivert at least 260-270 hp. Still it should have been faster.. But tomorrow I'm having my new propeller on, so we wil see :=)
 

steelespike

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If the boat was not on the trailer right. Perhaps hanging off the back a little If the bunks or rollers don't support it well it could deform the bottom.
May be quite subtle causing trouble as speed increases.The keel may be reasonably straight but the stern area of the bottom
may be pushed in. usually near the transom.
Some boats stored outside without sufficient cover might stand for months with water or ice inside eventually rotting the framing.
Also may sit in the slip with water standing in them for weeks or months.
Let us know if you find anything when you haul her out.
 

Chris1956

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OK, Sounds like you have a 305 cubic Inch Displacement (CID) V8 motor (Small Block Chevy). Yes they normally have 225- 250HP or so, depending on carb or EFI. Unless your motor is specially modified from stock, I would not expect a lot of difference from the older motor.

So a 21 footer with a SBC, should hit the mid 40's in MPH, I would think. I doubt you will make 50 MPH, but might get close, with the right prop and trim.
 

kallewell

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Tried with a new propeller today. This one was 14 1/4 x 22. We reached 52 mph, so that's better :) We will try with another one now, witg 23 in pitch to see how that works :)
 

steelespike

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When calculating ss props it is suggested to add an inch pitch in the calculation
If we assume 1.60 ratio a 22" ss prop at 52 mph = 20% slip.Too high.
if we could get 13% slip the speed would be about 56.8
If you go to a 23" prop calculated as a 24 using 4600 rpm(increasing pitch 1" usually lowers rpm about 200) guessing 20% slip we get about 52.
The high slip may be because the boat lays down too flat.Could also be a tach error reading too high.
Wouldn't hurt to test the 22 again and get an accurate wot rpm.
 

kallewell

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When we tried 22 pitch, the rpm was 4800-4850. At 4900 rpm you noticed the speed got lower on the indicator.
If we use 23 pitch now, we will lower the rpm with appr 200 rpm as you say.
You think that would be a better alternative?
As you says, at over 4000 rpm the boat lays down too flat. At 3000 rpm that is no problem, and you can feel the boat going easier on the water.
 

steelespike

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It appears that a 23" prop would make about the same speed as the 22" prop at wot.But at about 200 rpm less.
This would have no affect on the boat laying down too flat that appears to be related to the speed or perhaps trim not the rpm.
You might research for a prop noted for bow lift.
When you trim up the boat should get up on the water better.Each boat/setup has a maximum up trim that is affective.
Some boats can be trimmed up more than others.Some props can be trimmed up more than others.
A ss prop should grip well but an entry level ss prop may not do as well as a more sophisticated one.
You might try the 22 again and trim up very gradually waiting for each trim up to settle.
I have a feeling that when the rooster tail developed the rpm probably goes up and the boat settles and slows.
Is your speed by gps? The only sure accurate speed though if you have current or tides they need to be taken into account.
 
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kallewell

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The speed is on gps yes.
We have tried to lift the trim gradually, but when reaching 4850-4900 rpm the propeller starts to spin, and ofcourse losing speed..
After what we have experienced after changing some propellers now, it seems like the boat doesn't like cupped propellers.
 

steelespike

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Cupping is how you develop lift whether its stern or bow. Also can improve handling responce and grip.
You still should evaluate the hull.Your slip is at 20% thats close to what you would have with a big heavy pontoon boat.
Is the bottom clean and smooth? No peeling paint?No distortions?
 
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kallewell

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To be honest, the boat is not looking especially good under the surface. Paint is peeling all over. Think I have maybe ten layers of paint. My next thing to do in the winter, is to get it clean under :)
 

steelespike

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It's amazing how much speed is lost with a rough bottom.
Cleaninmg it up will give a good chance to check for problems.
 

jestor68

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The Well Craft site shows a 1997 2150 with a 5.7L Merc reaching 51.4 mph @ 4600 rpm using a 21 pitch SS Merc prop.

A point of reference never hurts.

This equals to a 17% slip value, which is not uncommon for a Well Craft boat.

More blades will provide more bow lift at speed. Think Merc Bravo One four blade 21 pitch.

Your "new" motor is likely rated at the crank versus the prop. Your boat is rated for a max of 250 hp at the prop.
 
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kallewell

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Maybe a four blade propell will help, so maybe I should have tried one. But I haven't got one now, in that case, I have to buy anotherone.. ;)
 

kallewell

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Steelspike: Which propeller do you think would be the best for my boat? Which will give highest topspeed ;)
3-blade 14 1/2 x 23 or 4-blade 14 x 21?
 
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