What prop on 18.5 bowrider

[snake91876]

i have an imperial deep vee bowrider that is 18.5' with a 3.0l merc that
is newly rebuilt. i have the alpha one outdrive and a 17pitch 3 blade prop
right now. Im getting nearly 4800 to 5000 rpms. i have ordered the smart
tabs for my boat to control some chine walking and porpoising hopefully. I
only get a top speed of 32 mph. the foam in boat is dry recently redone. should i go with a 19p to get more speed or a 21p. will the 21p be too hard to plane the boat with a 17p and doel fin almost stayed on plane always.

 

[Silvertip]

Re: What prop on 18.5 bowrider

Lose the fin, try a 19P prop and add the Smart Tabs. A 21P will pull roughly 800 RPM off the WOT rpm which then puts you into "lugging" territory and it will make hole shot absolutely terrible with anything other than you in the boat.

 

[steelespike]

Re: What prop on 18.5 bowrider

i have an imperial deep vee bowrider that is 18.5' with a 3.0l merc that
is newly rebuilt. i have the alpha one outdrive and a 17pitch 3 blade prop
right now. Im getting nearly 4800 to 5000 rpms. i have ordered the smart
tabs for my boat to control some chine walking and porpoising hopefully. I
only get a top speed of 32 mph. the foam in boat is dry recently redone. should i go with a 19p to get more speed or a 21p. will the 21p be too hard to plane the boat with a 17p and doel fin almost stayed on plane always.

It seems a little unusual for a 18'+, 3.0 I/O to both chine walk and porpoise,
at only 32 mph.I wonder if there is some bottom distortion of some kind?
Of course the fin may be causing handling problems and a speed reduction.While the 17 won't produce top speed I would think you should be able to get 38-40 with the proper prop.As long as you are considering a prop change you might check out the Hustler al. props they generally produce an over all improvement close to ss at al prices.

 

[cribber]

Re: What prop on 18.5 bowrider

I have a similar boat and engine combo and I'm running a 19x14.3 aluminum prop on a 3L Penta with the SX drive. Hole-shot is about 4 seconds and WOT trimmed up I can hit 43 mph with a full load. I'd go with the 19" pitch and that should bring your RPM down to the recommended 4600 rpm range for that engine size.

Another thing to check since you mentioned this is rebuilt... what gear ratio are you running? 32 mph seems very low even for a 17" pitch

Silvertip said it all...