livnluce

This isn't for a an offshore boat, but it is a general question about props. My Sea Ray 207 BR calls for a 15 3/4 x 17 C prop but I cannot find anyone who sells that size. The most common is a 15 x 17. Will 3/4 diameter make much of a difference? Should I go up to an 18 pitch if the diameter goes down 3/4 inch?

Thanks.

Nik

A.O. Razor

What motor and drive are you running? Gear ratio of the drive? What does the boat have on it now, and what speed at which rpms is it running? Don't worry about the diameter, your boat is not long and heavy. For all around good performace, I would run the Vensura in a 17" or 19". It's a 14" diameter SS 4 blade, a really great prop for the kind of boat.

livnluce

The boat came with two props. One appears to be in very good shape, but it is 15.25 x 21 pitch prop. I'm thinking that is a lot of pitch for this boat. The one on the boat now is quite banged up and it is 14 x 19 pitch prop. Neither of them are what the Sea Ray chart recommends, and the one needs to be replaced.

It has a 228 Mercruiser. I just picked up for a family boat for cruising and pulling a tube. It's winter up here so I haven't been able to put it in the water yet.

Nik

A.O. Razor

Nik

Forget the chart, props have come a long way since then. What year is it? Is it right to assume that you have a Generation 1 Alpha drive on it? I'm not very farmiliar with the 228 engine package. If you can post some data on the motor and drive ie. what rpms is it supposed to spin at wot and what is the gear ratio for the drive ect? That will help. You should consider bolting your 21" on, and see what happens. It is a lot easier to give advice with some baseline numbers.

The info needed is this and the first 3 are important:
Rpms WOT specified by Merc for the 228?
Drive gear ratio?
WOT speed @ ???? rpm with the current 19" and 21" props? (GPS speed is needed)
Make/model props you currently have?
Stainless or alu props?

With or without this info, I would say testing should be done for the good result, but the props to look into are: Vensura or the Mirage+. What pitch is not easy to say without the before mentioned info, but it will most likely be in the 17"-19" range.

If your local prop pusher can't help you with props for testing, Bblades have a test program, and finding the right prop is well worth the money. http://www.bblades.com/pressreleases...essReleaseID=3

livnluce

You are probably right. I may have to wait until spring and put the boat in the water with 15.25 x 21 pitch prop and get a baseline.

As far as specs on the 228. WOT is 4200 to 4600 rpm. The gear ratio is 1.50:1. The props I have now are aluminum and I may stick with aluminum for this boat.

Would you recommend going to a 4 blade or sticking with a 3, and why?

Nik

A.O. Razor

I will start by asking you, why on earth you want to stick with an alu prop??? Whether you go with a 3 blade or 4 depends on what you want to do with it. The 4 blade will have better mid range efficiency, lower planning speed and quicker time to plane. The 3 blade will be 2-5 mph faster when in cases such as yours, the x-dimension is low. If you want an alu prop, the Alpha 4 prop is a good choice for an all aound prop. In 16" pitch the dia. is 15" and in 18" pitch, it is 14.5" in dia. What max rpms are you spinning with the 19"?

livnluce

Well, I picked this one up used for $75. I think I'll put it on and give it a try. 14" diameter and 18 pitch 4 blade stainless. For the money, I figured I couldn't lose. If nothing else, it will give me a good base line to start with and the 19 pitch aluminum that I do have is beat to crap.





Nik

A.O. Razor

That should work quite well. I can't see what model it is, but the geometry looks ok. For 75$, that's not bad at all, looks clean. It will problably run rpms close to your 19". Whether it'll run more or less rpms, is hard to say. Shoot me a pm when you have had it on, I'm very curious to how it works.

Good luck with it.

livnluce

Thanks! And thanks for your feedback. I'll let you know how it goes once the ice melts here.



Nik

A.O. Razor

Yeah, I hear ya. 0-5*F outside as I write. Brrr.

You're welcome.