Marine Engines for Sailing

[Matthew]

Hello,
Wasnt sure whether this should be in the power, or sail section, so thought I would start here.
I am designing a small sailing yacht (lwl=24ft, loa 30ft) and have selected the yanmar 1GM10 engine as a suitable powerplant.
I know a bit about soiling and have designed a few dinghies, but never anything with an engine, so dont know the first thing about them.
The websites I have found for this engine arent the best for the beginner either.
Basically I am hoping due to space, to get away without any reduction gear, and a small prop. I know this isnt as efficient as a big, slow prop but I havent the space, and its only really going to be used in the harbour.
One website gave me the impression it had a built in gearbox? Is this usual for marine engines? If so, is the rated power and RPM the shaft output (ie after the gearbox) or the engine RPM?
Its quoting 3400 rpm at about 8 HP. WOuld this speed cause very short prop life due to cavitation?
Any thoughts, help or tips on this would be greatly appreciated.
Regards
Mat
Attached is an early Rhino Rendering of the boat so far...

http://www.boatdesign.net/gallery/data/512/353swallowboatsrhino-med.jpg (http://www.boatdesign.net/gallery/showphoto.php?photo=39)

[lockhughes]

Originally posted by Matthew
selected the yanmar 1GM10 engine as a suitable powerplant.
I know a bit about soiling and have designed a few dinghies, but never anything with an engine, so dont know the first thing about them.
Basically I am hoping due to space, to get away without any reduction gear, and a small prop. I know this isnt as efficient as a big, slow prop but I havent the space, and its only really going to be used in the harbour.

Got space for ballast Matthew? ie... batteries? Check out what's going on with the newest electric motors and batteries. Ask yourself, how, exactly, when and how and where the (non-sail)propulsion system will be used... and work on being able to handle a bigger prop.

Cheers

Lock
http://groups.yahoo.com/group/QCYCTender/

[Portager]

Are you planning to use your boat on the Red Sea?

Sorry, I couldn't help myself.

Cheers;
Mike Schooley

[Jeff]

Heck I think it is quite bold. Well, really bold. Nice model so far too :)

Once I rendered a model with a nice strong blue tint on the windows which I thought was a great water/sky reflection. The person I was doing it for however thought that I was proposing all the glass be gradient-blue tinted.

[Gades]

Hi Matthew,
nice boat you're working with.

By the way, is it an entry for the ClassicBoat Competition? or are you designing it for yourself?

[Portager]

Matthew;

Yes, you will need a transmission. 3400 rpm would be too fast to spin your prop and you will probably want reverse. For propeller and shaft information get a copy of "Propeller Handbook" by Dave Geer. www.Amazon.com has it.

The Yanmar brochure for the 1gm10 engine can be found at
http://www.yanmar.com/marine/pdfs/123%20GM%20INBOARD.pdf
sorry it is a pdf file. If you prefer you can access the specs at
http://www.oldportmarine.com/1gm10(V)_specs.htm and the figures at
http://www.oldportmarine.com/1gm10_sc.htm .

The power and rpm ratings for the engine are measured at the crank shaft, but the engine is generally sold with the transmission. The speed is reduced by the gear ratio and torque is increased by the gear ratio (except for a 2% to 3% loss). Since power is the product of speed and torque it is unchanged by the transmission (except for a 2% to 3% loss). The weights and dimensions include the transmission.

The Yanmar is a good engine, but you might also consider the Beta Marine "Beta 10" or BZ482. These are 10 and 12 HP Kubota engines. They are a 2 cylinder engine, which will run much smoother than the single cylinder Yanmar. The weight is 167 lbs for the Yanmar versus 183 lbs for the Beta 10. Length is the same at 21.81 in (554mm), width is 16.54 in (420mm) for the Yanmar versus 17.13 in (435mm) for the Beta 10, height is 19.09 in (485mm) for the Yanmar versus 20.16 in (512mm) for the beta 10. The Kubota is one of the only engines I know of with a better specific fuel consumption than the Yanmar. This means you will get very good mileage, but you will also get complete combustion which means very little diesel smell. The Beta 10 list price is $4,995.00

Here are some good web references for the Beta Marine engines.
http://www.rhby.com/betaengines.html
http://www.montegaeng.com/beta_ten.htm

Cheers;
Mike Schooley

[Gades]

Portager: that was a nice reply.
I just wanted to let you know that the link:

http://www.oldportmarine.com/1gm10(V)_specs.htm

needs to be modified in your post.

[Portager]

Thanks for the compliment and the clue Fernando;

I gotta remember to test drive them before I submit it. I corrected it and test drove them all so it should work now.

Cheers;
Mike Schooley

[Matthew]

Thanks Mike Schooley, for your reply.
I wasnt sure about the transmission being included in the drawings, was basically my point. ie is the length of the yanmar that you quote (554mm) including the gearbox?

I have some of Dave Gerrs other books, boat strength and The nature of boats, which are very good, excellent reading in fact, but never got the prop handbook as they havent interested me or concerned me at all until now.

Thanks to all of you for your comments though.

The Red sea is defintely a mistake n'est pas?!
Still reading my Flamingo manual....

[Portager]

The transmission is included in the drawings. The giveaway is that the crankshaft on the front end and the drive shaft on the back end do not line up. If there is no transmission the crankshaft will go straight through (it rotates better this way:)). If there is a transmission then there is usually an offset due to the gear pairs.

Sorry about the Red Sea comment. I just can't pass up a bad pun:) . Your boat looks very nice.

Cheers;
Mike Schooley