Monday, 29 July 2013

Engine Support

Serenity came with an old Mercury 6 horsepower, 2 cycle outboard. It was unreliable, required mixing the fuel, and the short shaft allowed the prop to lift out of the water when someone went forward. After having the engine cut out several times while trying to dock, a potentially dangerous situation, I went on the hunt for a new motor.

Original outboard and bracket. First launch in 2006.

The boat is small and light enough that a 4hp will do under calm conditions, but this being Newfoundland, calm is uncommon. A rule of thumb is 1 hp for every 500 pounds of displacement, so another 6 would have been fine. The deal I found, however, was on a new, but old inventory, Johnson 9.9 hp, long shaft, 4 stroke.

This new outboard weighed almost double the old one, and the original adjustable bracket struggled. The springs did little to help with lifting, and it had a lot of play which sent vibrations through the hull. Another upgrade was required.

In 2008, a new bracket was installed. This model has much heavier springs, making raising and lowering the motor almost effortless. It also has more substantial arms, so vibration transmission is lessened. I just should have bought one with longer arms. If not careful with positioning, the prop liked to take chunks out of the rudder.

New outboard and bracket in place. Preparing to launch in 2008.

I noticed a bit of flexing in the transom with the new setup, so in May of 2013 I decided to beef up the support backing and push the bracket back away from the rudder with a wooden spacer.

That 3M 5200 was difficult to unstick!
A test fit.

The block of wood extension was coated in Cetol, and then given a couple coats of epoxy.

Generous amounts of sealant were applied to the new 2" straps, and allowed to mostly set up prior to installation. I hoped it would help a little with vibration isolation.

New aluminum straps with sealant applied.

Accessing the nuts requires crawling into a cockpit locker and laying on the hull. It is a tight squeeze, and an unpleasant task for someone as claustrophobic as me.
The original straps

New straps, with the old ones on top. A significant size difference.

Then everything was bolted together with some fresh 3M 5200, and I was ready for another season.

Serenity now had a much more suitable engine bracket, better reinforcement for the mount, and the propeller was pushed just enough away from the rudder that I was no longer chipping little pieces out of it.

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