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Author Topic:   Doel Fin Disadvantage
lpaton posted 05-28-2001 10:27 AM ET (US)   Profile for lpaton   Send Email to lpaton  
After raving about my Doel Fin a disadvantage has cropped up. I hit a deadhead at relatively slow speed on the weekend. It hit doel finand cavitation plate broke off. The fin is pretty solid. I do not thonk that this sort of impact on the plate alone would have broken it off. I don't know if I will replace the fin. Broken skegs are not a big deal but the cavitation plate is another matter.
B Bear posted 05-29-2001 11:42 AM ET (US)     Profile for B Bear  Send Email to B Bear     
I am sorry to hear that has happened to you. You are only the second person I have heard of striking something and breaking the cavitation plate on the lower unit housing. I am glad it is not a common thing. It is a risk that is taken when adding on anything to the lower unit, even with those skag protectors. May be this is another reason it is recommended raising the engine so the fin is just at the surface. As with everything there are pluses and minuses, what ever we do, it is a calculated risk.
I hope that what ever part that broke can be tigged welded back on without much trouble.
triblet posted 05-29-2001 12:29 PM ET (US)     Profile for triblet  Send Email to triblet     
Here's number 3: A dive buddy of mine broke
the cav plate on the Honda on his inflatable.
He had a Doel Fin or one of the knockoffs.
He swears he didn't hit anything.


lpaton posted 05-29-2001 05:29 PM ET (US)     Profile for lpaton  Send Email to lpaton     
Hey Bear
Since you know I have to Tig a replacement piece back on maybe you have an idea on replacement and filler material? Was thinking of appropriate thickness aluminium plate and aluminium filler rod. Have to trim the lower unit up and could recover some of the jagged edge ai am cutting off and try to use as filler. Any comments?
lhg posted 05-29-2001 06:36 PM ET (US)     Profile for lhg    
Your damaged will be covered by insurance, less your deductible. I would get your lower unit fixed professionally. Maybe they'll give you a whole new gearcase housing.
lpaton posted 05-29-2001 08:08 PM ET (US)     Profile for lpaton  Send Email to lpaton     
My insurance has the equivalent of US$650 deductible in order to get a "good" rate of equiv. US$550 per year. The repair will be a professional one as long as I get the weld right, and should be a lot less than my deductable. Have sent out queries to several professional repair shops in the US for weld advice.
I would be surprised if insurance would go for a new unit if it is, as I gather, repairable.
Insurance company is Allstate.I will appreciate and consider however all advice before jumping into the repair (presently planned for Friday)
Dan posted 05-29-2001 08:31 PM ET (US)     Profile for Dan  Send Email to Dan     
Someone with a 20' Edgewater and a 200hp Yamaha with stainless prop hit something yesterday. He wound up putting a few dings in his prop and bending his skeg. I told him he should have the skeg looked at by a pro and check with his insurance company. The guy just pooh-pooh my suggestion, laughed and said it was "no big deal, I'll just wack that skeg back into shape." Well , today I happened to pass by the marina. There was his boat, with a fist-sized piece knocked off his skeg. Now, he'll have to get a weld repair, I guess. Personally, if it were my boat, I'd want a new gearcase housing. That way I wouldn't have to worry about the repair lasting. I think the guy was a jerk for hitting his bent skeg. Can't say he weren't warned.
B Bear posted 05-29-2001 08:47 PM ET (US)     Profile for B Bear  Send Email to B Bear     
I have answered Laird to the best of my ability. Working with metal had always fasinated me, from the first time I learned how to weld and became certified. Hopefully the insurance will take care of it, if not the weld will more than likely be stronger than the rest of the unit. The funny thing is that the boston whaler dealership, where I bought my boat had Doel fins for sale right next to the parts window.
DIVE 1 posted 05-29-2001 09:56 PM ET (US)     Profile for DIVE 1    
I agree with LHG about going to a professional. Welding lower units can be a tricky operation. We generally use a piece of 6061-T6 aluminum cut and shaped as a replacement piece. The filler rod needs to have a low melting point and compatibility with the base metal, 4043 works well. Care must be taken not to overheat and distort the housing. A lot of times the lower unit has to be totally disassembled so the seals do not melt or the lower unit oil burns. Most outboard shops remove and disassemble the lower unit, send it to a welding shop, and then reassemble after welding.
lpaton posted 07-09-2001 07:35 AM ET (US)     Profile for lpaton  Send Email to lpaton     
Thanks to all who helped out with info, especially B Bear. Had the cavitation plate repaired Friday. Used !/4" T6 with a 6061 (I think) filler rod.Placed piece of T6 over broken area and marked it from underside then cut out the plate on countour lines with plasma. Had to mill out circular slot to fit in the anode fin. Machinist had to play around a lot to get jig just rite.
Welding it back on was straight forward.After prepping edges at about 45deg welder tacked in place then welded from underside. Followed this with a back-gouge from top and did the top pass. After grinding one cannot see weld.
Now the interesting part. We kept the lower unit in place! ( was quite a feat backing the Outrage III into the machine shop). I wrapped the lower part of housing in wet rags and placed wet rags on opposite cavitation plate. I kept rinsing rags out in cold water as they got hot.
Rags worked well drawing heat out. Could place my hand on housing all around except weld area without burning. Used the boat yesterday and all seems fine. Welder is confident in his work. Was his first cavitation plate but he has been doing skegs for 30 years.
Thanks to all for advice
B Bear posted 07-09-2001 08:59 AM ET (US)     Profile for B Bear  Send Email to B Bear     
Thanks, I am glad everything worked out.

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