prop help please 20 ft w/260 hp

[dmweyrauch]

I have a 20 ft open bow sunbird 1984 with a 5.7 260 hp alpha 1 outdrive, There is a 21 pitch 14.75 alum 3 blade prop on it, Ittops out at 5500 rpm at 45 mph,using a GPS I dont want the engine to rev that high and that's the lowest rpm I can run to get 45 mph.I feel it should get more mph, That is just with me in it. I tried a 19 pitch 14.5 alum 3 blade prop, Then it revs way to fast and only 35 mph. What do you guys recommend.I still want decent low end to pull a skier.

 

[dmweyrauch]

Re: prop help please 20 ft w/260 hp

Can anyone help

 

[hidef]

Re: prop help please 20 ft w/260 hp

You went the wrong way on you prop selection. You should have gone to a 23" pitch. Every two inches of pitch will either increase or decrease the engine RPM by approximately 300 RPM depending on gear reduction. I figure the 19 raised your max RPMs to 5800 so going to a 23 should get your RPMs down to around 5200.

 

[dmweyrauch]

Re: prop help please 20 ft w/260 hp

I agree the oly reason I tried a 19 was because a friend had one to try, What are you thoughts on how fast the boat will go with a 23 pitch?

 

[Bondo]

Re: prop help please 20 ft w/260 hp

I agree the oly reason I tried a 19 was because a friend had one to try, What are you thoughts on how fast the boat will go with a 23 pitch?

Ayuh,... It'll All a function of prop design, hull design, trim, 'n horsepower...

The ONLY Given is the motor won't spin as fast...
The hull will probably go Faster, but it could go slower...

 

[75TowerOfPower]

Re: prop help please 20 ft w/260 hp

What's your gear ratio on the outdrive? Sounds like you have a goofy ratio like 1.8 ish. Normally a V8 in that size of a boat will have a 1.48 or 1.62 gears and use a 17P and 19P for water sports. So possibly a 23P 4 blade would work well for you keeping a decent hole shot (adding 4th blade) and decreasing your WOT RPM.

What lakes do you go on as well?

 

[dmweyrauch]

Re: prop help please 20 ft w/260 hp

We go to the maumee river, and lake erie, Indian lake, How can you tell what ratio outdrive a boat has? The more I read into props the more confused I get?