prop suggest
 

Hello;



We have troubles with next combination:
- Romar 19 Italyan boat with classic deep V, CG to much forvard.
- Suzuki year 2011, 100 HP, transmision ratio 2,59:1, cavitation plate 2" higher than transom bottom, but we have no troubles with cavitation.
- originall Suzuki propeller 14x22

Maximum rpm it is only 5.200 min-1 with one passanger and only 36 mph end speed. Weight of boat, engine, two passangers and 1/2 fuel tank it is 2.400 pounds.

Measuring with GPS give us next datas:
- 3.500 rpm = 22,5 mph - 20% slip
- 3.800 rpm = 25 mph - 19% slip
- 4.000 rpm = 27 mph - 15% slip
- 4.500 rpm = 31 mph - 13% slip


Any suggest what to do?
- engine it is impossible to mount lower, it is on the bottom bolts.
- we would like to improve end speed
- we would like to improve fuell efficiency
- we would like to improve start
- we would like to reach more rpm at wot.


Existing configuration it is originall from Romar factory.

New propeller...?

http://romarimbarcazioni.blogspot.co...0-bermuda.html

Unfortunately you will more than likely not see much additional performance with propeller adjustments. 1 mph with blueprinting of the propeller is possible.
You are somewhat limited with HP and a deep V boat. Adding HP or reducing weight are the best options.

Brett

13% slip at 31mph is actually quite good, if you want to go faster you need a bigger motor. The only thing you can try is to raise the motor up until you start to have cavitation or cooling water flow problems. Move up one hole at a time and see how it responds. If the prop is aluminum you could try a stainless steel model in the same specs but with a small boat and HP I doubt it will make much difference? Also the 4 things you want to improve it is impossible to get all 4, the setup that is good for midrange cruise may not be the best for top speed, the best setup for top speed may be slow to get on plane. You should make sure that the engine is getting into the max RPM range specified by Suzuki or you will have problems with it.

Hello;


Thanks for replyes.

Engine have wot betwen 5.000 and 6.000 rpm, we are on the bottom of this range, but inside.

In our case we have only cca 2.000 rpm on prop shaft at wot.

Prop shaft it is 6,4" under keel.

What to do to improve start? Smaller diameter or smaller pitch? (14" diameter on so small boat?)

Will be better for fuel efficiency in medium range, if we install prop, which will come on higher rpm at wot?

Smaller pitch will come on plane faster and increase acceleration. This may increase top speed by a mph or 2, it may not. Fuel economy at cruise will drop.

Brett

Thank you.

It would seem with your CG too far forward, that a larger diameter, and less pitch would improve bow lift, reduce slip, and increase both cruise and top speed. A round ear prop with tip cup, and more diameter would be ideal. You may want to try a 21" Mirage Plus.

see answers after you questions

Hello Thom,

Welcome to the board.
Your input should be interesting. I do want to suggest your advice on using a larger diameter on this particular application may be a little aggressive and non productive..
Larger diameter creates more stern lift and will hamper bow lift. 14.75" diameter large blade area propeller might take us backwards.
Smaller diameter and higher rake angle is better advice.

Brett

I am thinking exact round of this. My idea it was to pick up this prop on 13,5" and make heavy cup on blade ears to made "higher rake" and more bow lift. I am thinking, that smaller diameter with more cup will increase bow lift and this will increase hull eficiency. At the end will perhaps reach same or better slip with more rpm- better efficiency of combination. Is it possible that this scenario work?

Unfortunatelly we are few thousand milles from you Brett. In other case we would emediatelly order your test program and your labb experiences. In our situation, we will probably try to do this in my company.

Any comment round of idea for smaller diameter and heavy cup?