View Full Version : 1967 18 Classic trim tabs
ethyl
06-29-2009, 06:10 PM
Mine has no tabs, has been converted to a merc, beefed up 350 Chevy. She works well with two or three people but solo she porpoises quite a bit from 45 up to 65 and the throttle is not full. Bennett tells me that M120s will not stand the stress of 60-70 mph in a good chop and advise HD13 or HD16. If I can get by with the M120s this sure would save some expense but I want to "do it right". Any comments wil be greatly appreciated. This is a great site!
BlownCrewCab
06-29-2009, 06:57 PM
If you have to use bennetts, used the Twin Ram. a 12"x12" tab is actually too big for an 18' boat, but I think thats the smallest tab they have with twin rams.
Usually the porpoise goes away with speed, seems like yours is caused by it. Do you have a Hook in the Hull? are you trimming by feel or looking at a gauge?
osur866
06-29-2009, 07:16 PM
My 18 came with Bennetts and they are single ram think 12X9 maybe and I've never had a problem with them in rough choppy water of LOTO. I personally prefer the single ram tabs because they are more responsive than the dual rams JMO there. I use tabs at idle and when holding the boat on plane under 40 but above they are high and dry with no propise. Steve
ethyl
06-29-2009, 07:38 PM
Blown Crew, thanks for the reply. I trim by feel and look at the indicator backing off when the prop starts to suck air. I can't see an obvious hook.
ethyl
06-29-2009, 07:40 PM
osur866, thanks for the info. Do you have the "bat wing" tabs or the flat ones?
BlownCrewCab
06-29-2009, 08:03 PM
seems like you know what your doing and that your hull is in good shape. Have you tried any other Propellers? The part where it happens going faster gets me:nilly:. you have good power trim and know how to use it.. (or do You?) J/k.. if you where to trim to that point with the boat on the trailer how does it look? the Optimum trim setting isn't real high, I'd like to see yours. I assume your boat has a Tru V Bottom??? Mine had a sweet spot that was the drive Parallel to the bottom.. Do you have a bunch of stuff stowed away under the front deck? couple 100lbs worth?
ethyl
06-29-2009, 08:58 PM
Blown Crew, not much up front( two life vests) She had a fuel tank transplant before I bought( aluminum 24 or 25 gallon ). I know the 350 is heavier than the original mill. Maybe I don't know how to trim. I have tried every position. In a 6-12 inch chop with 3 adults aboard into the wind I can trim up until she sucks air and and back off and things are o.k. Some chine walking but not too scarey. I have an '82 18' Concord with a bit milder 350 that I trim the same way up to 70mph or so but have no porpoising. I will check the position on the trailer as I remember the indicator position to have been. I'm using a 25 inch Laser and have tried 23, 25 inch cleavers, 23 inch Mirage Plus, 24 inch Hydromotive, 24,23 inch Ballistic. The Laser and the 23 cleaver work the best of all. I have not tried a 4 blade yet. I'm thinking the trim tabs may be a wiser investment?
mattyboy
06-29-2009, 09:33 PM
a 67 18 is a little different from a newer one is this a sharp keeled barrelback??
ethyl
06-29-2009, 10:39 PM
mattyboy, The keel aft is slightly rounded and all the strakes come all the way back.
mattyboy
06-30-2009, 06:51 AM
if the strakes come all the way back and the keel is slightly rounded it sounds like a barrelback if the shape of the bottom looks more like a V and not a U and the top of the transom looks like a frown :garfield: it is a barrelback
port helm? merc rh rotation ? I would drop a line to scott pearson or cdma they have similar setups not sure what tabs scott used but i hear in that setup a little tab is dragged to help offset the prop torque when solo
ethyl
06-30-2009, 12:35 PM
mattyboy, yes,u shaped aft keel, barrelback, port helm, merc rh rotation. Thanks for your input.
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