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Size of outboard engine

I have a 24foot narrowboat with a 15 year old Honda 9.9hp engine. As I am on the Great Ouse plus Fens I feel I need to upgrade to a more powerful engine. I am told that the 15hp engine is the same as mine therefore do I need the 20hp Honda?

Asked by: Ken Hand  | 5.12pm, Thursday 15 October

WW says:

Whoever told you that the 9.9 and 15hp engines are the same may have meant that they use the same block but have different size cylinders within. The 15hp will certainly give you more power than your present 9.9hp - particularly if it is a much newer model. The question is, will it be enough?
If your boat was a 24ft glass fibre cruiser, the answer would almost certainly be 'yes'. However, since your boat is rather heavier and you are cruising on fairly open waters, a 20hp engine might be a better bet as it should give you more power going upstream and will get you going more quickly from a standing start.
If you decide to go for a bigger engine, make sure it is a Honda or another make of 4 stroke engine. Two-stroke outboards do not like ticking over for long periods in locks and the plugs tend to oil up. The engine then cuts out and is difficult or impossible to restart. I once owned a boat with a 15hp Chrysler 2 stroke outboard. I eventually swapped this for a Honda 7.5 four- stroke and found this just as powerful, much quieter and far more suitable for canal cruising.

Graham Booth  | 10.38AM, Thursday 22 October

The engine block for the 15hp is now shared with the 20hp engine- both are quite different to the old Honda 15hp block. The 8hp shares the block with the 10hp (and even that is a new design).
All 4 of the engines (if you choose electric start) come with 12A alternators- and Honda probably have the best charging rates in this class, giving around 6 A of charge at not much above tickover. The 15 and 20hp models also have optional electric tilt mechanism (though they are both rather heavy). You should achieve far better battery charging with the new Hondas than the old 9.9hp model.
Another consideration is the propellor. If you get a choice of props, then go for the largest diameter, with a small pitch. This will give you more thrust, which is what you need with a small narrowboat. Although props can be expensive, they can make a lot of difference- a dealer might be happy to do a straight swap for you, if you mention the use that they will have.

Mark Langley  | 12.10PM, Friday 23 October

Readers say:

Many thanks for your useful information. I shall certainly go for the 20hp engine.

Ken Hand  | 4.55PM, Thursday 22 October

Many thanks for the information

Ken Hand  | 12.47PM, Friday 23 October

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