I have a 36 feet timber displacement hull vessel currently using a 40 year old Yanmar 3ES low speed 50 HP engine and plan to replace this with Beta Marine diesel. Can I have opinions on suitable Beta replacement model please?
Can you please let me have the following information before I can make a suggestion. 1) What is the weight of the vessel? 2) what is the waterline length? 3) what size propeller can you use? 4) Is this a full keel boat with the prop in an apeture?
Here is some more information on the 40 year old all timber vessel. Weight 14.5 ton, water line length around 34 feet, full keel boat with prop in aperture, prop 26 inch x 13.5 pitch.
The original engine is a Yanmar 3ESDE and it has 4.58 litre displacement and provides comfortable cruise speed of 7 knots at 1100 RPM. Gear box has 1.93 reduction ratio (hydraulic).
You could use either the Beta 50 or the Beta 60 with the PRM260 transmission with 2.94:1 ratio. The prop calc give the following; Beta 50 with 2.94:1 - use 24"x16" three blade propeller with 50% blade area ratio. Speed should be 7.7Knots Beta 60 with 2.94:1 - use 26"x15" three blade prop with 50% BAR. Speed should be 8Knots. Either should give you a comfortable 7 knot cruise. The PRM 260 is a great heavy duty hydraulic transmission. These engines are much smaller that what you are used to but are still low reving by todays standards and have plenty of low speed torque.
Thank you for the prompt reply - much appreciated. I hope to be able to get started on the conversion soon and will most likely go for the larger engine.
One more question. Would it make sense to go for the 75 HP engine and lower the gear box ratio a little so I can operate at the best part of the torque curve? I expect to keep my boat for may years and want to do the best possible conversion. I also want to keep noise levels down and have some reserve power so keeping the revs down may make sense.
I want to keep the current propellor if possible but notice that the Beta engines rotate in opposite direction to my current set up. Will this create a problem or can the gear boxes offered be ordered for any direction of rotation ?
Any opinion? I have attached a picture of the vessel.
The 75 HP engine will not really gain you much and no matter which transmission ratio I use, you will end up with a different prop. The best bet is the Beta 60 with the PRM 260 2.94:1. This is a great transmission and can accept a left hand or a right hand propeller. All you would have to do is a slight re-pitch of your current prop.
Your boat looks great. Expect it to be a bit lighter after your repower and also to have lots of room to spare in the engine room. In real terms I would expect you to still cruise at 7knots but the Beta 60 is likely to be running at about 2,000RPM.
