How big an engine is too big for my motor sailer

[rileyatsea]

Hi all

I recently bought what I understand is the biggest of the colvic watsons 11m+ and while she's generally sound she needs an interior refit and I also want to replace the existing engine. This is a Status Marine (peugeot engine) XD4.9 which I understand is somewhere around 65Hp. My question is what size engine can I use and what are the pros and cons - I don't want anything less than what is in her but I wondered if there was benefit in going bigger and if there are problems apart from space if I do go bigger. I am thinking of buying second hand and I've been offered what I think is a nice 120Hp engine but I'm worried it's too powerful.

Also if any help, the boat is also very beamy (looks like a pregnant com when out of the water) and she weights about 10.5 tonne according to her papers.

Thanks

Riley

[TeddyDiver]

It's maybe just a matter of opinion, but reckon 120 is oversized..
I'm building a (THE) 10m motorsailer and got 71hp engine for that. Allthough planning to take up to 10hp to run something else than the propeller, 55 would've been about perfect..

[charmc]

There is a pretty successful design about the same size as yours, the Banjer 37. 11 m long, displaces 12 tons dry. According to the owners' club website, the original engine offerings were a standard 62 HP 4 cyl Perkins diesel, with the option of a 95 HP 6 cyl.

The website is here: http://banjer37msclub.tripod.com/techs.htm

Guillermo, a regular contributor to the forum, is an active member of the owners' club, with experience taking his Banjer 37 into the Atlantic. He's also a designer of commercial fishing boats. His comments would be helpful, as he has attended many of the banjer 37 outings and spoken with many other owners.

Given the 2 original engine choices, one with 50% more power than the other, and the fact that so many are still around after 40 years, it should be interesting to learn, if possible, the % of original sold with the larger engine, and what repowerings have occured over the years.

Personally, I'm inclined to agree with TeddyDiver that 120 HP is a bit much. Buying a used engine, however, often means compromise. If it will fit, and the fuel economy reported for similar applications is good, then it could be a good choice. Prop for torque and fuel economy, though, because the extra power will only give you an extra knot, a big wake, and burn lots of fuel otherwise. I used to live near Toms River, NJ, home of the importer of the Marine Trader line of displacement cruisers. Their standard engine for boats up to about 13 m was a Lehman 120 HP. Most owners are pleased with their fuel economy. Not an exact comparison, but maybe useful info.

[rileyatsea]

Many Thanks Teddy and Charmc - I think I'll have a look for something smaller than the 120.

Regard Riley

[FAST FRED]

Figure out the displacement in pounds , divide by 2240 to get disp in tons , and multiply that by 3.

This will give the number of the max practical HP the hull can use.

Pick an engine 20% more powerfull and your'e done.

FF