Need prop help for a Cruiser boat.

[ccustomrides]

Hey everyone.
Boat in question is a Sea Ray Sundancer 250 with single 5.7 alpha drive.
Well on my new boat I have a prop situation. I purchased the boat and the prop that was on it was little dinged up (alluminum) but nothing crazy. So I knew that real way to test it out was to use it and see where my RPM and Speed was.

So first time I took it out I had 2 people onboard and half tank. It got on plane ok for a cruiser and did about 27MPH WOT @ 4200 maybe 4300 RPM.
Next time I went out I had 6 people on board and half tank again. This time I had to send people in the cabin to get on plane and it ran WOT 4100 to 4200 RPM at 16-17 MPH. Now I know that I own a cruiser and it does have a underpowered setup being 5.7. My buddy has a 260 dancer and he told me out 5.7 problems and how boats this size have problems getting on plane and finding a prop can be a pain.

The guy I purchased the boat from gave me a spare prop. I go and look at the spare and its a Michigan wheel 16x16 prop. I was little shocked that 16x16 would be used on a underpowered boat of this size. Tell me if I am wrong but why would you run that big of a diamter?
So then my next step was to check the prop on the boat. Its in the water so it was a little tricky but after getting it off I got my answer and it was the same size as my spare. 16x16

Here is where the questions come in. Why would you run 16x16 prop and be turning less rpm to begin with. Then is this a special prop because 16p to me means a 4 blade and the 2 props I have are 3 blades. Next I went to Sea Ray website and they have a 15.25x15 pitch listed for my boat. This sounds more like it. Smaller diameter and smaller pitch. I just dont know why in a world you would put a big load like that on a alpha with a 16x16.
So should I get me a oem prop or stick with what I got. Also any people with same boat sizes? I just wanted to see what you guys run,rpm and speed. Any problems with people getting on plance,etc. In the end I know its a Sea Ray and they are heavy slow boats but I think my prop is way wrong. Thanks again.

 

[Silly Seville]

Re: Need prop help for a Cruiser boat.

The previous owner might have piloted the boat solo often enough to warrant a higher pitched prop to achieve a slightly higher top speed. Going back to the 15p will definitely raise your WOT a little bit. You won't see much of a difference in time to plane, unless you are the soul occupant while doing so. The bottom line is, it is a heavy, heavy boat for its length; and that's what makes it such a sea worthy hull. But it's definitely no ski boat. Have it weighed. Should be right about 6k lbs. with full tanks and three batteries.

 

[Maclin]

Re: Need prop help for a Cruiser boat.

A larger diameter prop when compared to smaller diameter prop of the same pitch digs in better, lowering slip and maybe easing a cavitation problem. Useful when the load is heavier and the drive needs more "traction".

 

[steelespike]

Re: Need prop help for a Cruiser boat.

What is the hp of this 5.7 it appears they run from 210 to 320. 320 seems a reasonable size for the application.
Also what is the gear ratio stamped on the outdrive.
The po may have liked cruising at displacement speeds and felt the 16X16 was most efficient.
Or as often happens decided on the wrong prop.
It does seem to me that a boat company wouldn't design a power train that at 15" doesn't leave much room for prop selection for excessive loads or high elevation operation.

 

[ccustomrides]

Re: Need prop help for a Cruiser boat.

I am not sure on hp I can look that up but I know my drive ratio is 1.5 and I have a 260 5.7 Mercruiser in that boat. When I took the prop off thats on the boat I noticed that the center section of the prop where the exhaust comes out was little dinged up. I think the blades looked ok. If I can get a good deal on Ebay for a 15.25x15 I will give that a try. I know some people run even 4 blade props on the same style boats. Boat dry weight is like 5500 so yes its a very heavy boat and in my opinion will be a dog with 4+ people on board either way. I just want to have more RPM and keep engine from loading up so much when I have extra weight.