Two engines

[oakleyb]

Does having 2 15hp engines provide the same power as 1 30hp engine, i ask as i i'm wondering about replacing single engine in prout

thanks

 

[RobWales]

Does having 2 15hp engines provide the same power as 1 30hp engine, i ask as i i'm wondering about replacing single engine in prout

thanks

No, from memory (but I stand to be corrected) due to double the drag with gearcases etc you can bank on two producing approx 20% less than one!

 

[Cookee]

The question has been debated occasionally on Rib.net - the answer is no, as Rob says there are some losses to take into account such as gearbox drag and mechanical drag - you would need at least 30% more total power to achieve the same performance although this was calculated for larger combined power outputs.

I would be looking at a pair of 20's in your case. The first thing I would look at is the rating for your hull in terns or power and weight to make sure it will still float!

 

[Twister_Ken]

I would be looking at a pair of 20's in your case. The first thing I would look at is the rating for your hull in terns or power and weight to make sure it will still float!

Stepping up from 15 to 20 ponies hardly makes a difference in weight terms. Approx 15kg per engine, in the case of Beta.

 

[Tranona]

Ignoring the strict power requirement, two engines will be much more effective on a cat as you can place them with the props immediately in front of the rudders improving low speed handling. You can also run on just one engine for cruising in flat water.

Downside is cost - not quite double a larger engine and drive leg (assuming you have a centrally mounted single) and space taken up in the aft end of each hull which may limit accommodation and access for servicing. Twin engines are the norm in today's cats, but most are 36' plus so the downsides are less than in older smaller cats with narrower hulls.

 

[Cookee]

Stepping up from 15 to 20 ponies hardly makes a difference in weight terms. Approx 15kg per engine, in the case of Beta.

There will be a bigger difference between one 30 and two 20's though - if it's on a sailing Cat I'm sure it will be fine - I was thinking of outboards on a RIB or similar ......... Same rules apply about output though

 

[TQA]

Make sure you get the saildrive versions that have different props suited for the needs of a sailboat.

EG http://www.tohatsu-uk.net/EnginesNew/SailDrive.htm

 

[boatmike]

Does having 2 15hp engines provide the same power as 1 30hp engine, i ask as i i'm wondering about replacing single engine in prout

thanks

In a Quest 33, 2 x 20 HP engines will be superb. Don't forget that you can always run on one engine especially when motor sailing. There is little weight penalty going from 15 to 20 so I would go for it. You will notice a big difference when punching a tide!

 

[oakleyb]

I do really need to replace engine and leg in the near future and feel the cost of a 30+hp beta and new sillette leg will be very nearly the same as fitting 2 smaller Beta's + plus all the positives on having two engines

 

[Ric]

Have you considered putting in two engines of different sizes?

When Dekker senior rebuilt his daughter's Gin Fizz for her RTW sail, he put in one Volvo of around 28hp, and a smaller Yanmar alongside of about 15hp. Each had entirely separate fuel systems. She used the smaller engine for motor-sailing.

Having said that, is a Prout one of those unspeakable dark-side machines with two hulls? In which case probably not a good idea.

 

[Tranona]

I do really need to replace engine and leg in the near future and feel the cost of a 30+hp beta and new sillette leg will be very nearly the same as fitting 2 smaller Beta's + plus all the positives on having two engines

Be wary of the additional costs of installing two engines from scratch. Two new sets of engine beds, two fuel systems, two exhaust systems, two props, two sets of controls etc.

 

[boatmike]

I do really need to replace engine and leg in the near future and feel the cost of a 30+hp beta and new sillette leg will be very nearly the same as fitting 2 smaller Beta's + plus all the positives on having two engines

And Oh! so quiet!!
Sillette legs are the invention of the devil and scream almost as loud...
You will find some additional cost but if you can do the work yourself like glassing in the saildrive leg bases etc, you will certainly have a better result and it will enhance the resale value considerably. I would certainly go for it in your position.

 

[oakleyb]

I was thinking of shaft and prop over sailidrive as i'd once viewed a quest 31 with this setup but guess saildrive install may be the best option.

 

[Tranona]

It is certainly easier to install as you don't have to worry about lining the stern tubes up, don't have extra water intakes to worry about and the engine ends up horizontal, and probably further back in the boat. Probably better to go for Volvo or Yanmar as they use their own saildrives and you can fot rope cutters to them if you want.

 

[TQA]

OOPS I had assumed you were going the outboard route. My bad.

I know of two Prouts in the Caribbean with the central engine removed and two outboards fitted. One has two old diesel Ruggerini outboards 15 hp I think, and the other two 9.9 petrol 2 strokes.

 

[grumpy_o_g]

Is it viable to replace the Sillette and engine with a single outboard, petrol or diesel?

 

[William_H]

Engines

Just be mindful that smaller engines may have less cylinders and will therefor be much noisier with more vibration. One three cylinder might be a lot quieter than 2 X 2 cylinder certainly a lot quieter than 2X 1 cylinder diesels. I would think 2x outboards would have a lot of attraction. good luck olewill