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candron
candron

Posted: Sun Aug 29, 2010 6:07pm

Post Subject: Replacing boat engine

Dear Tony I am thinking of replacing my narrow boat engine for a larger version. My boat is 57' and the engine I have at the moment is a Beta BV 1505 37.5 BH. I feel that at times the boat is a little under powered and I am looking around for other options. What do you think of the Thornicroft Kaizen range. I was looking at perhaps the T.105, or perhaps you could recomend an alternative engine type ? Would increasing the size of my existing prop be an option, I'v no idea of the size of my present prop, or how big I could safely use with my present engine. If I did change the engine it would be a self fit. Yours John

Tony-B
Tony-B

Posted: Sun Aug 29, 2010 7:40pm

Post Subject: Replacing boat engine

Dear John, I have a 54ft boat with about a 32bhp engine in it and it seems fine to me. It coped admirably with the Thames into Limehouse and the Thames in flood two summers ago. I can not comment on the suitability of the Thornycroft engine you mention because you fail to give its HP and I am not going to use my mobile broadband to find out. I suspect your prop may not have the optimum blade are and may be the wrong size. Before you do anything I would advise that you wait for your next blacking and at that time get the size from the prop. It will either be stamped between two blades or underneath the nut. Then contact Crowthers to see what they recommend. If this is an ex hireboat it may well be under propped to keep the boat speed down and the engine speed up to aid charging. Trying to guess a prop size without vast experience is a fools task. There is a propeller size calculator on Castle Marine's website but I fear it may not be accurate for inland canal work. Down load their prop calculator and play with it. The diameter is limited by the gap between your skeg and the uxter plate minus 4" ideally or 2" with a greater risk of cavitation. I would self fit and engine but my son,a music teacher, would be totally incapable of doing so without supervision so without knowing your abilities I can not comment. BY and large all the mainstream makes of engine are perfectly adequate engines. You should get the prop chaanged to suit a more powerfull engine. Tony Brooks

candron
candron

Posted: Mon Aug 30, 2010 5:54pm

Post Subject: Replacing boat engine

Dear Tony thanks for the information in your reply to my query. Just to say that on leaving school I spent five years in an agricultural engineering workshop working on tractor deisel engins etc and feel confident in undertaking a refit. {all be it many years ago}I undertake most mechanical jobs on the boat, with the exeption of electrics, this dark art I leave to the auto electrition expert that I have on tap. The Thornycroft engine T105 that I had in mind is 42.5 BHP with a PRM 150 gear box. Beta recomend a 17" prop for my existing engine I will have to wait and see whats on at the moment the next time its out of the water. Thanks again for your time John.

Tony-B
Tony-B

Posted: Wed Sep 01, 2010 10:01am

Post Subject: Replacing boat engine

If yours is a "typical" modern cruising boat I suspect a 17" prop may get too close to the skeg or uxter plate than is ideal. Personally I doubt you will notice much difference between the two engines as long as the prop sizes are correct. In neither case should you obtain anything like the quoted hp if you want economical and efficient operation. I suspect you will be spending about £1000 per hp gained. Tony Brooks

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