Outboard size for MFG 19? - Page 2 - SailNet Community
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post #11 of 14 Old 07-29-2008
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A Mac 25 is a much bigger boat. A 7.5 HP or 8 HP four stroke is an awful lot of weight to be hanging off the transom of a 19' sailboat.
Funny you should say that Dawg.. our little Hartley has a Johnson 7.5 that has been with the boat since the early 80's. Better not say that too loud - it might get upset!!

There is an article in the latest edition of Australian Sailing on this very topic and a few of us have had exactly this discussion to work out the smallest permissible outboard for the TS18 Class. The guidelines we were working to (from the Racing Rules) talk, not just about hull speed, but about maintaining hull speed into a 12kt breeze for 3 hours.

The end result was that, for an 18-20' boat, even though you could probably get to hull speed with a 2hp going flat-out, the smallest outboard you should have is a modern 3.5hp or old 4hp with around 15 litres (whatever that is in your currency) in fuel.

Remember: Outboards work best at 3/4-full throttle, so getting a big one is not necessarily better.

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post #12 of 14 Old 07-29-2008
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Yes, but I bet your 7.5 Johnson is a two-stroke, not a much heavier four-stroke, which is likely to be all the OP can buy nowadays.

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Originally Posted by Hartley18 View Post
Funny you should say that Dawg.. our little Hartley has a Johnson 7.5 that has been with the boat since the early 80's. Better not say that too loud - it might get upset!!

There is an article in the latest edition of Australian Sailing on this very topic and a few of us have had exactly this discussion to work out the smallest permissible outboard for the TS18 Class. The guidelines we were working to (from the Racing Rules) talk, not just about hull speed, but about maintaining hull speed into a 12kt breeze for 3 hours.

The end result was that, for an 18-20' boat, even though you could probably get to hull speed with a 2hp going flat-out, the smallest outboard you should have is a modern 3.5hp or old 4hp with around 15 litres (whatever that is in your currency) in fuel.

Remember: Outboards work best at 3/4-full throttle, so getting a big one is not necessarily better.

Sailingdog

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post #13 of 14 Old 07-29-2008
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Yes, but I bet your 7.5 Johnson is a two-stroke, not a much heavier four-stroke, which is likely to be all the OP can buy nowadays.
Yep, you're right on both counts

(Note to self: The Dog Is Always Right)

FWIW: Recommended four-stroke outboard size for Hartley TS18 = 4hp; Hartley TS21 = 6hp - although many use an 8 or 10..

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"Honestly, I don't know why seamen persist in getting wrecked in some of the outlandish places they do, when they can do it in a nice place like Fiji." -- John Caldwell, "Desperate Voyage"
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post #14 of 14 Old 07-30-2008
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The main factor I've found in choosing an outboard is its weight. For security reasons I have to lift the o/b off the transome, of my 20ft loa Sea Wych, and store it in the cabin! This can be quite an interesting operation/spectacle!....in the choppy Thames estuary off Britain's east coast. Hitherto, I had a Seagull Kingfisher 6hp 2 stroke (long shaft) for say 3 hours continuous motoring against a foul tide. I'm considering now, as earlier posts suggest, buying a 4 stroke 6hp for reliability, but what is the weight premium over an equivalent lighter 2 stroke? Also max (4 stroke) full fuel tank duration?
Cheers BS London UK
http:journals.aol.co.uk/spcdesign/BargainIssue
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