55.1 mph with 30 hp mercury

[tyst67]

I finally broke 55 mph in my racing flat bottom. I bought a mercury chopper 2 18 p and this prop is amazing. I know you guys think i might be crazy but my motor is to low in the water for running a chopper. My prop shaft is 2 and a half inches below the bottom of the boat and i still have some rpms to play with before i hit my rev limiter. How much more speed can i expect if i continue to raise my motor??

[chris3298]

How long is your boat?

[zul8tr]

Need these to estimate what you presently are doing

lower unit gear ratio
rpm with present prop

As far as what you can gain by raising the engine is a guess at best because many things come into play. Generally if the set up right you will pick up speed with raising the engine due to less drag. Only testing will tell. Pay close attention to cooling, slip in turns, rpm, handeling, speed at porposing.

There are other things to consider for greater speed besides raising the engine like trim angle, setback, weight distribution, etc.

Be safe wear a good life jacket and helmet if you presently do not.

[Mark75H]

Need these to estimate what you presently are doing

lower unit gear ratio
rpm with present prop

As far as what you can gain by raising the engine is a guess at best because many things come into play. Generally if the set up right you will pick up speed with raising the engine due to less drag. Only testing will tell. Pay close attention to cooling, slip in turns, rpm, handeling, speed at porposing.

There are other things to consider for greater speed besides raising the engine like trim angle, setback, weight distribution, etc.

Be safe wear a good life jacket and helmet if you presently do not.

Agree. Each of these things are important details that must be paid attention to.

[tyst67]

I know all these factors are important. Hitting 55 mph with a 30hp is super hard and ive been tuning it now for 4 years to get where i am now. My gear ratio is a 2:1 and Ive tried 2 different tiny tachs and cant get them to work for my rpms. I do know its screaming for a 30 hp twin mercury sea pro.(with a single carb)I understand all the different factors about boat trim and weight and setup but im not real sure what motor setback does. From what i understand more setback will give you more bow lift which would cause less boat surface in the water = less slippage = more speed. But I dont have any boat touching the water now so that really wouldnt do me any good to add more setback. oh yeah my boat is 14 feet long and 48 inches wide

[Jimboat]

I finally broke 55 mph in my racing flat bottom. How much more speed can i expect if i continue to raise my motor??

1. what is your rpm currently, vs. max rpm of engine?
2. can you send me a picture of your hull running at current top speed?

[zul8tr]

I know all these factors are important. Hitting 55 mph with a 30hp is super hard and ive been tuning it now for 4 years to get where i am now. My gear ratio is a 2:1 and Ive tried 2 different tiny tachs and cant get them to work for my rpms. I do know its screaming for a 30 hp twin mercury sea pro.(with a single carb)I understand all the different factors about boat trim and weight and setup but im not real sure what motor setback does. From what i understand more setback will give you more bow lift which would cause less boat surface in the water = less slippage = more speed. But I dont have any boat touching the water now so that really wouldnt do me any good to add more setback. oh yeah my boat is 14 feet long and 48 inches wide

That would be interesting to see a pic of your boat running without touching the water! I think you mean very little touches the water?

Set back does allow a greater moment arm for bow lift due to the engine weight farther back from the transom and in combination with trim angle promotes quicker bow lift. It also allows higher engine jacking since there is greater water spray uplift to feed the prop and cooling ports as it leaves the bottom trailing edge. Result is you can probably run more pitch and might have greater speed if prop correctly selected!

[tyst67]

here is a video http://www.facebook.com/video/video....51656727700405

[MWhite]

how fast u say that boats running, 55mph

[HTarver]

What I would do is, put a nose cone on it and raise the motor up till the center of the prop shaft is level with the bottom of the boat and you will see more top end. Also a good 6 inch jack plate will help and unlpug that rev limiter, you did say ''race boat'' . But I dont know how u race, in a cicle or drag? I dont know nothing bout going in a cirlce.