Diesel Outboards

[Paul]

I am considering buying a new outboard for my 4.0m searider. I was wondering about a diesel outboard in place of my 40 hp yamaha 2 stroke. Diesel is cheap and widely available at marinas. Does anybody have any experience or views as to whether this is worth considering. I presume that ther must be disadvantages as they would seen more commonly.

[GraemeCooper]

Hi Paul

It is some years since I dabbled into Diesel Outboards - but I don't think things have changed too much - in that they are very heavy for their power output - and I do not believe that they are a viable option for a 4 metre RIB. I think the only ones that would be within the weight limits are the small HP one made for canal and river use - which would not give out the power needed for a RIB.

Willng to be proven wrong though .....

[Paul]

I thought that there must be a good reason otherwise everyone would be using them.

[Powerboat]

Hi Paul,

My opinion would be the same .

Diesel outboards are too heavy really.

Have a look at 4 stroke petrol .

I run 3 Lencraft Lynx 6.8 metre RIbs

Two of them are fitted with Yamaha 115 hp 2 stroke engines and burn about STG £ 40 of petrol per day on an ISA Level 2 Powerboat Course

One of them is fitted with a Yamaha 100 hp 4 stroke and burns Stg £9 per day on the same course ( Petrol is about Stg£0.50 per litre here.

Performance on the 4 stroke is slightly less on the 0 to 60 but top end speed is similar and the four stroke is really quiet

Best wishes ,

Stuart
www.powerboat.org

[Paul]

Thanks powerboat. 4 strokes sound a lot more economical than my 2 stroke. With an average sea, one gallon will get you 8 miles equating to about 3 gallons per hour. What size four stroke do you think I should get, and which manufacturer do you think is the best?

[Powerboat]

Hi Paul ,

well...............I am still a firm believer in Yamaha ( although they are begining to price them selves out of the market in the last year or so ).

The main thing to check when replacing a 2 stroke with a 4 stroke is the weight difference.

This is where Yamaha score points . Most of their 4 strokes are designed from the ground up and therefore weigh more or less the same as their 2 stroke sisters .

Some manufacturers ( eg Honda ) use converted car engines and so end up with a very heavy engine with a poor power to weight ratio.

I recently drove a 6 metre Geminii with a 130 Honda which I feel would have been much faster and economical if fitted with just a 90hp Honda ...Some times more is less !

Check out the weight of your current engine and then check out the weight ( and price ) of a Yamaha 40hp and 50 hp 4 stroke .

I would reckon that a 40 hp would be oodles of power for a 4 meter RIB .

Best wishes ,

Stuart
www.powerboat.org