What would give me more top end?

[jsaylor]

24ft Tahiti Day Cruizer 454 engine 1980. I'm currently running a high 5 17p at 4000 rpm I'm running about 45mph.
More top end from:
high 5 17p or
4 blade 19
Both blades stainless
Thanks

 

[rallyart]

Re: What would give me more top end?

At that RPM with that engine you are not going to get more speed by increasing the pitch. You are already below the optimum RPM range for the engine. You might pick up speed by dropping pitch to let the engine run faster. Going to 4 or 3 blades would likely help also

 

[Bondo]

Re: What would give me more top end?

Ayuh,... What drive ya runnin',..??

Yer Over-proped now...
Ya need to get the rpms Up...

 

[jsaylor]

Re: What would give me more top end?

Drive is an Alfa one, not certain on drive ratio, I can by the way exceed 4800 rpm with my high five 17p

 

[Robbabob]

Re: What would give me more top end?

Drive is an Alfa one, not certain on drive ratio, I can by the way exceed 4800 rpm with my high five 17p

That little bit of information really helps. It appeared you could only reach 4000, thus, the statements you were over-proped. How much over 4800 can you achieve? Seems you need to do some testing.... the 4-blade 19P may bring it down a little, but not sure if enough without knowing what rpm you can achieve at WOT now.

 

[jsaylor]

Re: What would give me more top end?

I could certainly exceed 5k, Every thing is great as far as getting on plane and being able to stay on plane even at slow speeds, very little bow rise, I couldn't ask for more. I was thinking a sleek 4000 lb boat with 430hp would be a lot faster, I would however rather have the low end, Just wonder how much of this I would give up by gaining more top end.
Thanks

 

[Robbabob]

Re: What would give me more top end?

Check out these test results and see if there's anything of value for you, http://forums.iboats.com/showthread.php?t=218877.

Increase your pitch and you'll see that baby get more speed.

Your increase in speed will eventually show a reduction in hole-shot. However, testing is the only you'll find where that point is. I guess the good news is that you're not lugging the engine, but you're also not running as efficient as you might.

 

[jsaylor]

Re: What would give me more top end?

I tried switching from my high 5 17p to my 4 blade stainless 19, while getting on plane or shortly after my rpm's would rise however not pick up speed, it seemed like it would slip. Is this called prop wash? how do you eliminate