What prop should I use? I am new to owning a boat.

[arrivawaker]

Hi I just bought a boat for cheap and it had a 5.0 in it but the owner was dumb and failed to winterize it this last winter and put a hole the size of my fist in the side of the block and cracked the exhaust manifolds. I curently have the manifolds at a local metals shop to be welded and I am building a 5.7 to replace the 5.0. I have never owned a boat but my dad has so I am not new new to boats. But I dont know much about what prop to use and I have heard that elevation can effect the prop that you use so here is my question. I am mainly going to be using the boat at lake powell and a lake near me called highline. Highline lake is at an elevation of 4600 ft. I am wondering what prop would be the best for a quick launch and not rob to much of my top end speed? I will tell you a little more about the boat in case it will help.

1989 Bayliner Arriva 20 ft that will have a 5.7 with an alpha one. The 5.7 will have a little more hp than a stock 5.7 but not too much. The boat weighs about 2500 lbs and is a 20ft. If there is any other info I need to give you let me know. Thank you!

 

[BonairII]

Re: What prop should I use? I am new to owning a boat.

You'll need to know what your rpms are @WOT before a prop can be recommended.

 

[arrivawaker]

Re: What prop should I use? I am new to owning a boat.

I kind of figured that I was just wondering if anyone had a similar set up that might give me a recomendation because the boat has a 17 pitch 3 blade that came with it and it is so tore up I threw it in our scrap bin lol. So I am going to need to start some where and there are alot of props on our local craigslist but I have no idea where to start.

 

[Silly Seville]

Re: What prop should I use? I am new to owning a boat.

I curently have the manifolds at a local metals shop to be welded

That's a worrisome statement...

With a mild 350 and a 2500 lbs. load...I would say that you could easily get away with a 21p prop. That would give you the greatest top speed anyway. If you want a quicker launch, well then drop to a 19p. Might as well have one of each anyway for a back up.

 

[arrivawaker]

Re: What prop should I use? I am new to owning a boat.

That's a worrisome statement...

Thank you for the answer! The exhaust manifolds had about a six inch crack in each one above the two center bolts and the shop is a business that we do a lot of business with and we are very good friends with. They said they have welded them before on their own boats and have not had any problems with them afterwards and I know they wouldnt lie to me about that. Or did they? And also do you know if altitude would have any affect on what prop to use or would it mainly just be tuning the engine for that altitude because thats what I was mainly thinking.

 

[jestor68]

Re: What prop should I use? I am new to owning a boat.

Horsepower loss: HP loss=elevation X .03 X HP at sea level/ 1000.

 

[arrivawaker]

Re: What prop should I use? I am new to owning a boat.

Thank you I think I am looking at a hp loss of about 35 then to run it at 4600 ft.

 

[jestor68]

Re: What prop should I use? I am new to owning a boat.

Given all of the unknowns here, I would suggest you start with a Solas Rubex 4 blade 14-3/10 X 19 for good hole shot and decent top speed(mid 40's).

That's a fairly common prop size, that shouldn't be hard to sell if it turns out you need to adjust pitch from there.