| Author |
Message |
    
ian summerfield
Member
Username: budgie14
Post Number: 61
Registered: 06-2009
| | Posted on Monday, October 26, 2009 - 01:28 am: | 
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hi,i would appreciate some ideas about these [i call them permatrims] trims that are mounted on the cavitation plate.i know what they do,but are they recommended,do they really improve boating?wouldnt the manufacturers have fitted them from new ,if they were that good.any help would be good,thanks |
Strata
Member
Username: strata
Post Number: 24
Registered: 06-2009
| | Posted on Monday, October 26, 2009 - 06:07 am: |
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Had one on my old 16 footer, found that it helped get on the plane quicker but made it harder (and more unpredictable) to steer. I took it off. I guess it probably depends on what it's fitted to.... |
Fastjeff
Senior Member
Username: fastjeff
Post Number: 6996
Registered: 09-2003
| | Posted on Monday, October 26, 2009 - 06:45 am: |
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They tend to break off parts of the cavitation plate!
Jeff |
Graham Lamb
Senior Member
Username: galamb
Post Number: 6017
Registered: 05-2007
| | Posted on Monday, October 26, 2009 - 10:37 am: |
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I have played with them (mostly to see if the claims they make are true since alot of questions do come up) and as noted above I found the following:
They do get the "nose" down alot quicker so the boat comes on plane faster.
They really like to have the boat run in a straight line - especially noticable with a tiller model, so if you are making alot of (turns) it's like trying to steer your car in a parking lot with either standard steering or a blown power steering pump.
When you do go into a turn however, the boat really "hangs on" so it may be desireable for ski/board boats - you can do some pretty tight turns at higher speed without the boat (sliding) out on you.
As Jeff notes, they do put significant stress on the cav plate. I have never had a first hand problem (yet), but a few mfgs (Suzuki comes to mind who also built the small 4 stroke Johnsons) have had more than one busted cav plate due to aftermarket "fins".
I have never noted any "improvement" in fuel economy as a result of their use (one of the big selling points if you believe the writing on the package).
Mercury has basically no opinion on whether they are valuable or not and does not advise on their use either way - however, if it was a new motor and you ended up with a lower unit problem (during the warranty period), I'm sure they would be able to link the issue to your "aftermaket retro-fit".
After all my horsing around I have found they have a very specific, limited use for the average boater.
I like them if you have a smaller boat, with a lower horsepower motor (under 25 horse) and travel significant distances in no wake/controlled speed zones such as canals - by keeping the stern up/bow down at "lower speed" they really help with visibility - but can't really think of another "feasable" application.
If you "need" a fin then what you really need is trim tabs that go on the boat itself - these fins are just a poor man's (poor) alternative.
Next up the ladder would be products such as "smart tabs", which cost about 100 bucks and are a far superior alternative to the cav plate mounted fins (my opinion - every boat longer than about 16 feet should have trim tabs)....
Last thought - Merc, BRP/OMC, Yami, Honda etc spend millions in research and design. If cavitation plate mounted fins were a good/valuable product and drastically improved things, don't you think they would have incorporated them into the design of at least one model by now???? |
ian summerfield
Member
Username: budgie14
Post Number: 71
Registered: 06-2009
| | Posted on Friday, October 30, 2009 - 05:00 am: |
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Thank you for all the input.i recently bought a 2001 40 merc from a dealer,with 3 month warrenty,and the motor already had it on,so unsure whether to keep it or what.it makes it hard for putting the motor in a bucket for flushing.so now ive removed it.thanks again |
jamie campbell
Advanced Member
Username: outboard_doctor
Post Number: 711
Registered: 02-2009
| | Posted on Sunday, November 01, 2009 - 12:06 am: |
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Hydrafoils fix problems with poor boat design...I refere to lifting the bow very high into the air as they get over the hump.
If your boat does lift the bow excessivly a hydrofoil will cure it and allow the boat to stay on the plane at a lower speed.
However if your boat doesnt lift the bow excesivly fitting one to your boat will give it undesirable handlling qualities.
It will make the bow plough through the water and in a following sea your boat will be prone to broaching.
There is no gain in fuel economy and i speak from experience...i have fitted hundreds to many boats and their owners reported better boat performance and no gain in fuel economy.
Outboard manufactures in the 90's widened the cav plates on most models. |
Tony Delio
Senior Member
Username: tonyob
Post Number: 1641
Registered: 05-2001
| | Posted on Sunday, November 01, 2009 - 11:09 am: |
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It is better to trim the boat with ballast in my opinion. |
Alan Fisher
Member
Username: pilot481
Post Number: 54
Registered: 07-2009
| | Posted on Monday, November 02, 2009 - 03:30 pm: |
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Just wanted to add my experience with a hydrofoil. Ive got a 24ft Fiberform crusier with a chev 194 il six. I use a 16-13 prop and mercrusier outdrive. This is a heavy boat with a small engine. Adding the hydofoil made this boat feel much more powerful and much easier to control. Comes up on plane quickly and smoothly and does not adversly cause any problem with steering. So yes, I totaly agree that it simply depends on your overall situation. |
