Where are the prop experts?

[TheFormerlives]

Here's a question. I've got a 100hp Evinrude on a 16ft Procraft fiberglass boat. Right now, according to the tachometer, I'm turning 4800rpms at WOT and GPS'd the speed at maximum of 37mph. Its got a 17pitch stainless prop. My question is can I change the prop to gain more speed out of this rig? I feel like a 100hp should put me into 40-43mph or so.

 

[Willyclay]

Re: Where are the prop experts?

The prop experts are in the prop forum. You need to post up there. Good luck!

 

[Bob_VT]

Re: Where are the prop experts?

I will move the post.

If your tach is accurate you should actually be running at 5500 and it means you are lugging the motor.

How old is the boat and motor? Have you weighed the boat and measured it vs the stock weight?

You might have water in your hull trapped in the flotation.

 

[steelespike]

Re: Where are the prop experts?

I think you have more problem than a prop.
!7 is about right and you should be at about 5,500 and solidly over 40 as you suggested.
I would suspect a motor problem. Does the throttle open all trhe way.
good compression? recently tuned?Bottom clean and smooth?
Does the boat respond to trim?

 

[TheFormerlives]

Re: Where are the prop experts?

Sorry, didn't even realize there was a prop forum!

Anyways, the engine is a 1988 and the boat is 1989. I think its rated for 1750lbs fully loaded with gas, engine, gear and passengers. Normal operating weight would be just half a tank of gas and me plus the engine. I don't really know of a way to weigh it out of the water.

I bought it from a marina and they said it was all checked over and checked out fine. I'm fairly certain the throttle opens all the way, is there an easy to tell for sure?

It does respond to trim, I'll gain about 200rpms by trimming up properly and gain about 1.5mph

Haven't done a compression check, but as mentioned it came from a marina so I'm assuming it checks out alright.

 

[GETNWET]

Re: Where are the prop experts?

Check your speed with a GPS you may be going faster than you think.

 

[TheFormerlives]

Re: Where are the prop experts?

The posted speed was via GPS. Yesterday I had it out and I took off the hydrofoil that was on it, opened up the throttle a little more and trimmed up. I spun roughly 5200RPMS and hit 40.5mph with myself and another passenger. This is with that 17p stainless prop. I think if I raise the engine a hole, switched to a 19p stainless prop and went out by myself I might hit 45mph and roughly 5000RPMS