Gas engine in a displacement hull

About inboard or outboard motors.

Moderator: Bill Edmundson

Post Reply
User avatar
Posts: 50
Joined: Sat Jul 16, 2016 7:52 pm
Location: Rochester NY

Gas engine in a displacement hull

Post by Scot2640 » Tue Aug 30, 2016 1:41 pm

I'm still plugging away at my zip, having a great time but I still dream of bigger things. I'm looking at some of the big crusing plans here on Glen-L and some considerably more expensive stock plans from George Buehler (diesel duck, NW cruiser, Ullin 45). I'm reading and researching about various types of engines in a displacement hulls. I know conventionally speaking large cruisers have diesel engines. Period!

Why? Diesel engines are not made how they were use to, they are getting smaller and lighter, pushed by various environmental restrictions.

Is a 100 hp diesel the same as a 100 hp gas engine? granted I'm not an engine guy so talking about torque and rpms goes over my head. Am I understanding that the 100 hp gas engine would have to generate higher rpm's to get the same power as the diesel? Higher RPM's, more heat, more wear less reliability?

If I build a big boy that will be a coastal cruiser or looper, running between 5-9 knots is the considerably more expensive (buy and maintain) diesel really the only way to go. All these questions are based on a 20000 to 35000 pound displacement hull.

please and thanks!
A ship is safe in the harbor, but that's not what ships are for.

User avatar
Posts: 681
Joined: Mon Jun 14, 2010 7:16 pm
Location: Catheys Valley, CA

Re: Gas engine in a displacement hull

Post by steveh41 » Tue Aug 30, 2016 2:48 pm


Here's a pretty good and honest discussion of gas versus diesel in marine applications:

For the size range you indicated (10 to 18 tons displacement) diesel is going to be the way to go. Fuel economy, range and safety will all be positively impacted by diesel power. It's true there are high output turbo diesels out there, but there are also more traditional heavy-block low rpm engines (e.g. John Deere Marine or Lugger) which will give you all the advantages of a traditional bullet-proof installation good for the long haul.


The longest journey begins with a single step… then repeat as necessary!

User avatar
Bill Edmundson
Posts: 11377
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA

Re: Gas engine in a displacement hull

Post by Bill Edmundson » Tue Aug 30, 2016 3:38 pm


I agree with Steve. A normally aspirated diesel is almost bullet proof! And, cheap to run.

Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

User avatar
Posts: 898
Joined: Sat Mar 19, 2011 2:50 am
Location: Pine Mountain . Vic . Australia

Re: Gas engine in a displacement hull

Post by jenko » Tue Aug 30, 2016 4:20 pm

I agree also (long stroke small bore )diesel engine

User avatar
Posts: 4621
Joined: Wed Nov 12, 2003 5:25 pm
Location: Coastal Georgia

Re: Gas engine in a displacement hull

Post by kens » Tue Aug 30, 2016 6:32 pm

That little gas banger in my boat has been very good.
It is a garage overhaul of my own tinkering, and I have shown it no mercy. It is still going.
It has really taken a beating from me. Raw water salt water cooling too.
with that said, the same engine in a trawler should work fine.
Mount a 3:1 gear on it, and could work.
I would not be afraid of it.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

Post Reply

Return to “Boat Power”