Prop selection

[Gamba39]

Hello all new to the platform. I’ve done quite a bit of google searches which always seem to lead me to these forums but never and exact answer so I figured I’d ask my question directly here. I have a 99 Vip 184 with the 3.0L mercruiser and alpha one outdrive. I’m running a 5 blade 13 3/4 x 23P prop. With full tank of gas and four passengers(myself, wife and two five year old daughters), At wot i’m running 37mph at 4500rpm . I’m wanting to know if changing to a 3 blade prop would get me a little more speed and if so what size and pitch would be recommended, or should I be happy with what I’m getting.

 

[porscheguy]

It sounds like you’ve got a high 5. Speed demons they’re not. You’ve got 25% slip which is really high. A laser2 or an enertia would both likely gain you a few miles per hour, maybe more. 41-43 is probably the upper limit in terms of speed you’ll see on that engine. You’ll have to come down in pitch to a 21. You’re already 300rpm off your max rpm. Reducing the pitch and the number of blades will buy you the extra rpm you need, reduce your slip, and help you go a bit faster.

 

[Gamba39]

I appreciate the reply. I should mention I tried a buddy of mines 4blade 14x21 prop this past weekend which is what the mercury prop calculated said I needed and ended up losing RPMs and top speed. I ran 34mph at 4200rpm wot. He said it could have been the diameter being too big. Any suggestion on what diameter I should be running.

 

[jimmbo]

How do I get more speed, is always the first question every boater with a 3 liter engine asks... Best most realistic answer is, a bigger engine.

You might get a bit more speed by removal of all unneeded ballast, ie: wife, kids, mother in law(especially the mother in law);
Are you using the Power Trim for best performance?

The Five 5 while it does have 5 blades, the blades are smaller than a blade on a 3 or 4 blade props

What is your unit gear ratio?

A 3 litre could have a WOT range or either 4200 - 4600. or 4400 - 4800, depending on the year. Is there a Decal on the engine, or flame arrestor? It is very important to know that range. 4600 rpm(top of one spec. middle of the other) would be a safe number if you can't get the info.

I would recommend trying a 3 blade 23 just to get a baseline. Brand? I feel the merc/quicksilver props are about the best choice, when it comes to quality and engineering.

 

[QBhoy]

Porsche guy is spot on here. A 23” is a bit much for that set up. Only reason you are slightly in the rpm range is because it’s a high 5. You go to a 3 blade 23” and you will almost certainly be dropping out the rpm range and will be a dog out the hole. Go to a 21” good 3 blade and all will be well !

 

[Sea Rider]

For a spot on prop maximization need to know the exact wot rpm range factory stated for said motor. Running middle wot rpm range will achieve slight more top end increase with less hole shot performance, running max wot rpm range achieves top hole shot with slight less top end speed decrease. If deck load remains same, when the fuel tank is nearly depleated both scenarios will gain slight more wot rpm increase, rpm variation will depend on the fuel tank capacity number of gallons that can store.

When changing current prop to a much different one, will be extremely lucky to dial top prop performance on first attempt, usually it's achieved on second if not on third one depending which of both boating scenarios you'll like boating with.

Boating perfection could be costly if without a free prop exchange. The good thing about top prop maximization is that's done once under trial and error, from there on boat happily forever.

Happy Boating