New Motor Mount

[Steve Sanford]

All~

I just finished a new motor mount for (I think) a Duck Wrangler for another Long Island gunner/site member.

The owner noticed that the existing mount was still secure along the transom....

...but was coming away from the stern deck beneath each of the knees.

I took the old mount north with me at the end of October.

Is it just me - or is that old mount begging for help????

The original mount was exceptionally heavy - almost 35 pounds. (My replacement is about 15 pounds.)

Close inspection showed that all 4 through-deck fasteners were failing/had failed. The forward fasteners were bolts that had been embedded in the knees.

The aft fasteners were lags into the knees. In both cases the wood had failed (probably rot from moisture that made its way through the 'glass).

The screw clamps from the 25 HP outboard were not secured - so the OB mount was bolted through the motor board.

The wood beneath the clamps seemed spongy.

Here is the new mount ready for epoxy sealing and 'glass. It is setting on another vessel (2-man layout White-Wing) just for the photos.

The new mount is mostly AC plywood laminated and put together with epoxy. Fasteners are stainless steel.

The cleats inside each knee are Black Locust. Each cleat was scribed to the deck contour on the Wrangler and also beveled.

The entire mount was sealed with several coats of epoxy. The inside joint (which is a lap joint) between the knees and the transom board were reinforced with 3 layers of cloth and thickened epoxy (as in stitch-and-glue method).

It is now ready for installation. The original transom carriage bolts can be re-used. I chose hex-head bolts for the knees so that wrenches could be put on both ends when drawing it down during installation. I used a regular flat washer beneath the hex head and a fender washer beneath the backer boards.

The backers are 1/2-inch AC plywood - sealed with epoxy. I bored the 2 holes oversize (3/8-inch holes for 5/16-inch bolts) in the backer to make assembly easy.

Installation should take about an hour - and a tube of 3M 5200.

This heads south via USPS or UPS later today. Long Island's "Second Opener" is December 5th.

All the best,

SJS

 

[Pete McMiller]

Steve,

Just realized why I as well as everybody else on here love your posts. No matter if a project is simple or complex you always make it look elegant - thank you.

 

[Tom Scholberg]

From someone who has heard the awful splash of a motor parting company, nice job. One of the best features of this forum is the sharing of ideas and methods. I always enjoy your posts and attention to detail.

 

[Carl]

Wow, that was one of those cases of what you cant see could really bite yah in a$$ and the wallet.
Nice work Steve, as usual.

 

[steve schrat]

Looks great Steve a real piece of craftmanship, I will post a picture of it when I get it mounted,Your the best!!

 

[Eric Patterson]

That is a nice repair/upgrade. Should last as long or even longer than the boat.

 

[joe Sarrantonio]

Steve - As usual excellent work & excellent post, but is it possible in the future you can be little more specific and include some photos with a little more detail.

Happy Thanksgiving to you a your family.

Joe

 

[RLLigman]

Steve, the first thought that came to my mind, as you detailed the water intrusion damage, was the faulty design. There was no avenue for water drainage for any water that accumulated on the aft decking area between the two bracing pieces, essentially pooling any and all moisture along the base of the motor mount above the knees. Now, toss in a few years of use and freeze thaw cycles to allow that accumulated moisture to expand an "work" on separating the seal between the transom and motor mount. You did a very nice job of providing a drainage solution in the replacement mount, as well as strengthening the bracing arms and adding the backing plates.

When the Clark brothers were making the TDB-14', they cut a shallow relief channel into the motor mount plate running laterally immediately above the mating surface with the transom to enable any runoff to drain quickly. When I bought my first TDB in 1992, the first two things I did were to inject a thick bead of 3M 5200 around the hull/deck junction to ensure a good seal and deny water penetration along the entire joint, and then pull the motor mount board and reseal it. I added bracing plates (two pieces of 1/4" aluminum plate on the interior side to lend some additional strength to help handle the 25hp Yamaha.

 

[Steve Sanford]

Good morning, Joe~

In order to provide more detail photos, I'll have to buy more film - just as soon as the Fotomat opens....

All the best,

SJS

 

[Steve Sanford]

Good morning, RL~

Actually, there were scuppers where the knees met the transom board - but they were quite small - easily clogged with the inevitable bits of Salt Hay, Eelgrass and feathers that seem to make their way even around meticulously maintained vessels like this one. So, I made the scuppers significantly larger.

The entire assembly had been covered with 'glass mat. Although I cannot be certain, I am guessing that the resin was polyester (because, as you know, most mat is chemically incompatible with epoxy resins). I am thinking the excessive weight of the mount could be due to saturation/waterlogging from moisture that made its way through the polyester resin matrix. As the photos show, the wood around the fasteners had deteriorated - either from dry rot or freeze-thaw.

I am confident that the new mount will serve for many seasons, but I still wonder what "state-of-the-art" materials would be best. Stainless steel would certainly work - but is not within the skillset of the staff here at Pencil Brook Boatworks. I have never used Starboard or the like. Although rot-proof, I wonder how its structural properties compare with wood.

Happy Thanksgiving !

SJS