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Old 07-20-2014, 10:40 PM   #11
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I would think the 5.0 would have less torque than the 5.7 and would need less pitch to get the same rpm.

I was at the marina and my friend was out all day so I did not get to talk with him.

I like you prop idea selection. Let us know how it works.
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Old 08-16-2014, 03:26 PM   #12
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I've tested a 14,75 diameter and a 15P 4 blade and the rpm didn't change much.
The new prop has a smaller diameter and pitch but I couldn't get the rpm increase I thought a should, only about 100-150rpms more.
Theoretical I should have got about 400rpm increase.
Now I wonder if I do something wrong to get to the top rpm.

When I accelerate the leg is fully in and I give full throttle,
When boat is heavy loaded I use the Trim tabs to help her up in plane.
As soon as she reaches plane I push the trim tabs back up again.
After a while I reach the limit for what I can achieve whit the leg fully trimmed in.
Now to the point when I trimming the leg out, theoretical I would get a increase in rpm due to less boat in water and therefore easier to push the boat forward, but that ain't happening.
The engine rpm stays the same and the speed too.

I've been easy on the engine and maybe reduce the throttle a bit to soon,
But I have also read that I can run on wot to long and if I do that May result in engine damage.

What the heck is wrong, is it me or the boat?
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Old 08-17-2014, 01:12 AM   #13
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So you went from a 4 blade 16 P prop to a 4 blade 15 P, correct? If so I would expect about a 200 increase in rpms which is what you said you got. What is the current WOT?

Running at WOT for long periods of time will shorten the life of the engine.

Try keeping the trim tabs lowered, I do and use them to balance side to side loads depending on number of guests.
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Old 08-17-2014, 06:56 AM   #14
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I also changed the diameter of the prop from 15 to 14,75 four bladed, according to the propshop I could expect about 400rpms increase, maby they gave me the wrong info,

When I tested the boat before the prop change I was alone maby 20gallon of fuel and normal gear on board the wot rpm was about 4000,
When I changed the prop and tested we had packed the boat for a three day trip and was a bit heavier than the first test, now I reached 4100 again.
I thought that this small change was because the boat was heavier than the first time, but I got a feeling that if the boat is so sensitive for change in weight some thing is clearly wrong with me or the boat,
I've read that some have more people on board and still reaches a good wot,

For what I understand a unloaded boat should reach the higher rpm in the wot recommendation, when it do a heavy load will still keep wot in recommended rpm,
If I just make the engine reach the lover rpm in the scale the engine will work to hard when she's loaded for a week on the sea.

If I change my prop again to reach the recommended wot of 4600rpm I would have to buy a prop that have a 12 or 13P prop and that feels like the wrong way to go.
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Old 08-17-2014, 12:05 PM   #15
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Frankly I think a 4 blade prop is robbing the top end. A 4 blade give a better hole shot and low end performance however that extra blade is drag and will impact top end, additionally you have a 2 bbl carb so this also impact HP and torque that this engine is capable of.

What speed and rpm do you typically cruise at and are you happy with how it performs there? If you want better high end performance I would try a 3 blade prop.
I have the same boat but with a 5.7LX (4bbl) and a Bravo 2 drive and typically run at 3800 rpm doing 34 mph.
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Old 08-17-2014, 01:58 PM   #16
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Most of the time I cursing around in 7mph but sometimes I also cruising in 27-30mph but never faster than 32mph at this pion the engine revs about 3100-3500 rpm if I remember correctly this might be a bit higher with the new prop.
If the engine wouldn't take any damage of working with to much load due to wrong prop or lack of hp/torque I wouldn't care that the wot only is 4100rpm, but I want the engine to work in the right condition, hopefully that will make the engine not break down.

Maybe if I buy a three blade 14 1/2 x 17 that's mounted from the beginning it will work better,
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Old 08-17-2014, 10:04 PM   #17
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I think the 3 blade prop will get you the correct WOT, however I do not think the current prop will cause any damage with the way you are running the boat.
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