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Author Topic:   Trim Tab Mounting on Montauk
dogfish2 posted 12-17-2001 10:16 PM ET (US)   Profile for dogfish2   Send Email to dogfish2  
I recently posted regarding the subject of "porpoising," and after all the information sorting, decided to get the Lenco Trim Tabs, 12x9 edge mounts (recommended by Lenco) for the Montauk. However, there does not appear to be any type of solid backing, wood or otherwise, on the transom of the Montauks. Do any of you have any experiences with the mounting of trim tabs, and do you think that the pressure exerted by water on the tabs would cause the screws to pull out of the glass? I anxious to try these tabs but want to be cautious with the mounting. Thanks for the suggestions.
Bigshot posted 12-18-2001 10:10 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I think that is why you do not see them on Montauks! I may be wrong but I think you need to return them due to they will rip out if no wood is present.
llewellyn posted 12-18-2001 11:07 AM ET (US)     Profile for llewellyn  Send Email to llewellyn     
I'd look at all other possible solutions first, including calling Chuck Bennett at Whaler customer service.
gunnelgrabber posted 12-18-2001 01:49 PM ET (US)     Profile for gunnelgrabber  Send Email to gunnelgrabber     
dogfish2,..look up where triblet tells about mounting a swim ladder.the bottom attachment point is the deal...there's nothing there!..chuck builds "an inside the skin " pad,puck or mounting point...good luck..lm
triblet posted 12-18-2001 07:06 PM ET (US)     Profile for triblet  Send Email to triblet     
There's supposed to be "wood" in SOME places
on the transom, port side for mounting the
swim ladder, starboard side for a kicker, in
the middle for the main motor. The "wood"
is actually "WhalerWood" which is a phenolic
laminate (think REAL THICK Formica).

My problem was that the "wood" for the swim
ladder had moved forward and weren't stuck
to the back fibreglass like it was supposed
to be, and the cavity between had filled
with foam. The dealer fixed the first one
on warantee, I did the second and third
screws myself because it was less of my time
(dealer is a three hour round trip, two
trips = six hours). And it took two weeks
when the dealer did it.

I really don't think trim tabs are necessary
on my Montauk. It will porpoise at full
speed (requires really flat water) if I trim
the nose up too much. So I trim it down.


kingfish posted 12-19-2001 09:49 AM ET (US)     Profile for kingfish  Send Email to kingfish     
I've been following but not getting very involved in the threads about Montauks and porpoising, but I think Chuck has hit the nail pretty squarely on the noggin (someone else in an earlier thread may have come pretty close too). I've had a couple of Montauks, one with 100 hp Mercury and one with 90 hp Evinrude (originally '84, re-powered with '99), and spent a fair amount of time in both, low speed and high speed.

I can't help but wonder if there may be a difference in definitions or expectations here that are fueling your desire for tabs, dogfish2. My experience with my Montauks is that on relatively smooth water, when my goal was simply to go as fast as my boat and motor would be able to go, I'd mash the throttle, and slowly increase the trim of the motor until either 1.) the prop would start to blow out (speed would decrease and RPM's would increase, possibly beyond the recommended high end), or 2.) the boat would start to porpoise, as Chuck and you both report with your respective boats. Then I'd back off the trim (that is I'd trim the motor down)until either the prop bit, or the porpoising quit. *That* speed (the speed recorded after the prop had gotten hold again, or after the porpoising had stopped)is what I considered the top speed of my Montauk to be. In both cases my top end (non-GPS) was between 40 and 45 mph, and that seemed adequate. I never considered trying to tame the porpoising in order to attempt even higher speeds; I just believed that the degree of motor trim that caused porpoising was beyond that in which the particular boat and motor combination were stable. By the way, I had Doel Fins on the motors of both Montauks, and wouldn't do it differently if I had the chance.

My concern with using trim tabs on a Montauk to tame porpoisong at extreme high end speed, as opposed to using them for lateral trim and/or maintaing slower planing speeds without dropping off, is that you may be setting up a condition of instability that the designers never contemplated. I would really wonder if, with the rounded deadrise at the transom of a Montauk, that when the tabs were set to raise the stern even further out of the water (bringing more rounded hull surface into contact with the water forward), there wouldn't be an extremely slippery condition when trying to go stright forward. I would think there would be no chine touching, just the rear surfaces of the tabs and more or less of the rounded hull bottom. My expectation of that condition at high speed would be for the boat wanting to jig and juke and not necessarily respond to the helm as you would desire or expect. I could be wrong, but I could foresee someone cranking the helm over even further when it didn't respond, until something caused a chine to grab, and then with the motor at an ugly angle to the chine at high speed, a sudden and possibly disastrous high side event.

Just my long winded 2 cents.


Bigshot posted 12-19-2001 10:15 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I'm with you on that and like I said before, i have never needed them. I have even removed the doelfins because I don't try and plane at 12mph:). I have owned 11 Whalers and only one(model) with a porpoising problem was the 13 sport. Anymore than a minor trim and she'd bounce all over the joint. 17's and 15's never had problems and always had max hp. To each his own but shooting a rooster tail does not mean you are going faster, it means you are pushing the stern down and the water up and thus causing it to porpoise.
gunnelgrabber posted 12-19-2001 11:48 AM ET (US)     Profile for gunnelgrabber  Send Email to gunnelgrabber     
i certainly agree with all of you .a montauk doesn't need tabs..and i've never seen them on one...what i thought df2 was asking was"how to make a hole down there" to mount the tabs or whatever ...on that part of the transom.the low hole on a swim platform (which i envisioned as the same area more/less) foam wood!..regret any confusion on my garbled reception ....lm
dogfish2 posted 12-19-2001 01:03 PM ET (US)     Profile for dogfish2  Send Email to dogfish2     
All of your feedback and ideas are appreciated, and "Kingfish" probably hit the nail on the head when he brought up performance expectations. I am very pleased with the normal peformance of my boat, which is comparable to "Kingfish's", and was trying to find a compensator for the restricted performance caused by the bow mount trolling motor. Thus, the choice was Doel-fins which did not help, trimn tabs, or accept laws of physics and hydrodynamics and run a little slower whenever the trolling motor is aboard.

I think that all of you boating fans understand the "winter mindset", that is, when the weather makes you claustrophobic, you think of doing things to improve preformance just to keep your mind occupied.

Happy Holidays to all of you, and will let you know when I find a sollution.

kingfish posted 12-19-2001 03:11 PM ET (US)     Profile for kingfish  Send Email to kingfish     

Understand "winter mindset" all too well - during the winter, when Outre' is relegated to the Coverit shelter until Spring, if I can't find anything on board that needs doing, I'll start messing around and moving stuff until I break something, just so I can fix it!

Happy Holidays, and keep us posted-


Richard Quinlivan posted 12-22-2001 12:00 AM ET (US)     Profile for Richard Quinlivan  Send Email to Richard Quinlivan     
I have a '95 Dauntless 17 which has a mid speed (30 mph) porpoising problem if I trim it up where i think it should be. I improved the situation by raising the motor as high as it will go. I also have considered tabs and have the same question as dogfish2 - Will the screws hold satisfactorly in the fiberglass of the transom? I would be interested in a response from Tabman also.
Tabman posted 12-22-2001 12:18 PM ET (US)     Profile for Tabman  Send Email to Tabman     

How did you know I would be watching this thread? Just kidding!

A couple of points: One (not the only) reason a boat will porpoise is that so much of the boat is coming out of the water when it is up on plane that it will not have sufficient contact with the water flow to create the lift needed to maintain a stable condition. In other words it starts to “fall down”. When it starts to fall down more boat comes in contact with the water flow, creating more lift and the cycle starts.

Also any weight at the bow will make porposing worse. Keeping weight towards the center of the boat is better. To envision this imagine two equal weight kids on a seesaw or a dumbbell supported by a string in the middle. Push down on one end lightly and the dumbbell or seesaw will start rhythmically oscillating and keep doing it for a while until it stops.

Now imagine the kids or the weight of the dumbbell concentrated at the center (pivot point) and give it a little push. The oscillations will be much less and last for far less time. This is why weight in the bow can actually make porposing worse instead of curing it.

Using Trim Tabs to stop porposing works very well. The trick is to deflect The Tabs in very short bursts until the porposing subsides. What this accomplishes is having the surface of the Tabs just kissing the water flow. As the boat stats to sink (bow coming up) the Tabs will come in more contact with the waterflow and generate more lift, holding the stern up and resisting the cycle starting. Simply having the longer running surface created by the Tabs will help preventing porposing. The slight drag created by the Tabs in the water flow may scrub off a very small amount of MPH if the porposing is occurring at higher speeds. But is usually worth it. Since the Tabs are just kissing the water they will not create a dangerous “over trim” condition. But like all things on a boat the best safety feature is prudent operation by the driver. Always use Trim Tabs in small bursts when operating at higher speeds, and give the boat a couple of seconds to settle down before making additional adjustments.

As far as attaching to a foam cored transom, you guys likely know more then me. We sell lots of Tabs to Whaler, but of course they have made accommodation for them in the boat’s design. I did oven a whaler back in the early ‘70s but that was way before I worked for Bennett so no Tabs. But like most thinks I have a few thoughts:

The mounting plates for the Tabs themselves are so low on the transom that the screws are ususlly not even going into the core. Rather they are going into the layup for the bottom of the boat or the fillet that makes the radius where the hull bottom and transom join, so the screws may be in solid glass at that point (but like I said I haven’t cut a Whaler open lately so you will know more than me).

Also keep in mind that the forces on the mounting screws for the Trim Plane are mostly in shear vs. trying to pull off the transom as the Tabs lift the stern. The Mounting screws for the actuators (rams) are also mostly in shears as the actuators are actually being pushed against the transom when the Tab is lifting the boat. It is only during high speed reversing maneuvers will the screws experience a force trying to rip them straight out.

There are ways to firmly mount screws into a foam cored transom that on the boat you re talking about would likely be just fine.

I hope this helps,
Tom McGow
Bennett Marine

Dick posted 12-22-2001 02:28 PM ET (US)     Profile for Dick  Send Email to Dick     

I am not in need of tabs on my Whaler but I think it is great that a representative of a manufacturer is willing to post on this forum. It's nice to have input directly from a manufacturer. To few are willing to do it.


EasyE posted 12-22-2001 04:23 PM ET (US)     Profile for EasyE  Send Email to EasyE     
Yes it is great. Now all we need is the Boston Whaler CEO...Johnson master mechanic...Yamaha master
JohnAz posted 12-22-2001 07:54 PM ET (US)     Profile for JohnAz  Send Email to JohnAz     
When ever i attach anything to my whaler,,transom or otherwise i drill out a hole and insert a wooden dowel ,,& epoxy it in place 5 min epoxy works well enough,,then cover the dowel end with "Marine Tex",, colored corectly,,then drill a hole in the dowel and screw away...the biggest "plug" has been for a console 4 x 4 x6 inches..
kingfish posted 12-22-2001 08:57 PM ET (US)     Profile for kingfish  Send Email to kingfish     
I put tabs on my Outrage 22 which, like a Montauk, doesn't have a solid transom where the tabs and actuators are fastened. BW recommended reinforcing the transom at both places by opening up the transom from each side and scrounging out the foam and replacing it with wood embedded in a thickened mash of epoxy and chopped glass.

I believe that is the right thing to do, but it was too complicated for me, so I took a couple of short cuts. I wound up scrounging out the foam from holes I cut in the back side of the transom at the actuator brackets, that were small enough that I could cover them with teak pads that were just a little larger than than the actuator brackets themselves. I scrounged foam out of the transom in an area considerably larger than the holes, probably at least 4" or 5" in diameter. I formed the openings in the transom closed and filled the voids with epoxy from small "chimneys" I drilled down into the voids from the top of the transom. This has to be done carefully, slowly and with the right kind of epoxy to avoid a thermo-chemical reaction that'll ruin your day.

I felt, as Tabman said, that the hinge brackets were close enough to the layup for the bottom, and also as Tabman said, since the screws were largely in shear and that the greater forces were imposed at the trailing edges of the tabs, that they would be all right without further reinforcement. And I was a little shell shocked after taking a crash course in thermo-chemical reactions. Mine have held fine for a year now mounted that way.

I do think that it is important to reinforce at the actuator brackets in some significant fashion though because both the shear and impact forces are far greater there than at the hinge plates. I think without reinforcement at the actuator brackets there is a real possibility of compressing the outer transom skin as well as elongating the screw holes from the shear forces.


FISHNFF posted 12-22-2001 09:25 PM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
Thank you Tabman for answering some of my questions. I have the same problem as Dogfish2. My 17 Alert/Montauk/90 Merc4s will porpoise badly when I have my bowmount Motorguide installed. The Gatormount and motor weigh over 60lbs., and when mounted will cause severe porpoising if any positive trim is used. Without the motor mounted I can do 38knots GPS with gear in freshwater. Add the motor and I can get about 33 knots tops. Trimming will get me to 37+ knots with severe porpoising. I put the livewell(160lbs) in back and I have placed the Group 30 battery all over the place. I have even run with a 28 gallon fuel tank in front of the console without the porpoising. I will probably go with tabs also, for the porpoising problem and for trimming the boat laterally when running in a quartering sea. I realize all the comments about trying to make a boat do things other than what it was intended for, but what I am hoping for is a Whaler which will run well with a trolling motor mounted on the bow without the motor trimmed all the way in. I know there are those who will cite excessive motor weight (386lbs.) as the problem, but those with 2 strokes with kickers, especially those with stern mounted batteries, must surely have as much, if not more weight in the stern than I with my 4s on the transom and the batteries in the console. I do have a Doel-Fin and the motor is on the third hole up running a 17" Ballistic prop. The second hole had identical results, so I just left it on the third.
dogfish2 posted 12-23-2001 11:33 PM ET (US)     Profile for dogfish2  Send Email to dogfish2     

Thanks for the informative and convincing facts on trim tabs. It's always beneficial to have a professional clear areas of doubt and confusion. I, too, appreciate you "listening" to our questions.

Merry Xmas to all!


Richard Quinlivan posted 12-24-2001 06:33 PM ET (US)     Profile for Richard Quinlivan  Send Email to Richard Quinlivan     
With respect to tabs mounting on my 17 Dauntless I don't think that the screws will penetrate to the foam core. I think that the fiberglass is quite thick there. I just wonder how the screws hold in the glass? How long are they? Whaler has tabs as an option on several larger boats. How do they do that?

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