Small engine options

[Anthonyexmouth]

Thinking about changing the engine in my cygnus 19 open boat. Currently installed is a Volvo md17d which is a bit over powered and thirsty for the boat. Was re-engined by previous owner from an 18hp. Id like something as small as possible around the 16-20 hp range that would hopefully allow me to slightly raise the deck and make it flush with scuppers and remove the need for an engine box. Current engine has a 300mm high engine box.

 

[Bajansailor]

Anthony, could you maybe post a photo or two showing the current arrangement?

I googled the MD17D - it is 36 hp.
https://www.maritimepropulsion.com/files/pdf/1001243
When the previous owner fitted this engine do you know if he changed the propeller as well?
If he didn't, then that could be one reason why the engine is thirsty?
Can you reach maximum revs ok, or do you go beyond max revs?
I guess your cruising speed would be about 5, maybe 6 knots (?) - what are your operating revs at this speed?
Re making the deck flush - does the engine box get in the way (re tripping over it?)?
It will be quite a big job to raise the deck.

 

[Anthonyexmouth]

Anthony, could you maybe post a photo or two showing the current arrangement?

I googled the MD17D - it is 36 hp.
https://www.maritimepropulsion.com/files/pdf/1001243
When the previous owner fitted this engine do you know if he changed the propeller as well?
If he didn't, then that could be one reason why the engine is thirsty?
Can you reach maximum revs ok, or do you go beyond max revs?
I guess your cruising speed would be about 5, maybe 6 knots (?) - what are your operating revs at this speed?
Re making the deck flush - does the engine box get in the way (re tripping over it?)?
It will be quite a big job to raise the deck.

Max revs are are about 2800 but usually run about 1600-1800, anything after that just makes more noise and no speed. Pretty sure it's the original prop, currently tiller steering but considering changing to hydraulic steering via centre console so that's the reason for wanting to lose the engine box. Compensate for loss of deck space to the console.

 

[Bajansailor]

If you are going to build a console, then you could maybe have the engine under the console itself? The console would then essentially be like a larger engine box.
What speed do you get at say 1600 rpm? She should be fairly frugal on fuel at these revs, and if you fitted a smaller engine, and run it at higher revs to get the same speed, then there might not be much fuel saving?
Have you got a photo or two of the boat that you can post?

 

[Bigplumbs]

Is that a boat that could take and outboard or would that be completely wrong

 

[Anthonyexmouth]

Is that a bot that could take and outboard or would that be completely wrong

Outboard? I don't hate myself that much. Lol.

 

[Anthonyexmouth]

If you are going to build a console, then you could maybe have the engine under the console itself? The console would then essentially be like a larger engine box.
What speed do you get at say 1600 rpm? She should be fairly frugal on fuel at these revs, and if you fitted a smaller engine, and run it at higher revs to get the same speed, then there might not be much fuel saving?
Have you got a photo or two of the boat that you can post?

Engine is too far forward to do that. Get 4-5kts between 1600-1800 rpm. Prefer to have easy access to the engine too rather than build on top of it.

 

[Bajansailor]

It is nice to see that Cygnus are still going strong - here is a link to their 19' boat.
Cygnus GM19 | Cygnus Marine Boats

Re a helm console, does it have to be on the centreline?
I am thinking it could be on the port or starboard side of the current engine box, and then you would still have good access to it?

What do you use the boat for? Pulling pots, or just pottering about, or.....?

 

[Anthonyexmouth]

Potting, trawling , handlining want as much deck space as possible. With the engine being quite far forward it's a real pita with the engine box. That's why I want a flush deck, if possible. The centre console is to make shooting the trawl easier by losing the tiller.

 

[Bajansailor]

Is your engine further forward than what is shown in the general arrangement drawing below?

 

[Anthonyexmouth]

Is your engine further forward than what is shown in the general arrangement drawing below?

View attachment 123867

Yes

 

[Bajansailor]

How much further forward?
Is it between frames 3 and 4 (counting from the bow)?
The engine in the GA is between frames 4 and 5.

 

[Anthonyexmouth]

yeah, between 3/4. it's an original cygnus, when they were still made by Cygnus

 

[prv]

Raising the whole deck, and hence anything on top of it (you, but also fishing gear by the sounds of it) might be a concern from a stability point of view?

Pete

 

[Bajansailor]

@Anthonyexmouth I have taken the liberty of posting details of this thread on the Boat Design Forum in the USA, to see what responses will be generated on the other side of the Atlantic (and elsewhere) - here is a link :
Cygnus 19' GRP displacement fishing boat in England - a question re the engine

Have a look occasionally and see if anything interesting has been posted. And I will keep tabs on it, and relay any posts over here as well.

 

[Bajansailor]

Rumars on the BDF has responded with this post :

The MD17 is 689mm tall (HD versions 740mm). The modern replacements are all around 5XXmm, so that shaves around 150mm, or half his engine box height. The other 150mm can probably be had with a combination of adjusting the propshaft angle, moving the engine further back and raising the floor, but it's a lot of work for not much gain.

Modern diesel engine heights: Beta 16&20hp (Kubota) shallow pan 519mm, normal pan 560, Lombardini 18&27hp 522mm, Sole (Mitsubishi) 17hp 542mm.

Another option would be to modify an engine to work in a horizontal position (oil, exhaust, cooling, etc.) which is as much work as before, just of a different kind.

If the use case fits (range, speed) he can go electric, that fits all under the existing floor.