Hi John.
You have a similar design to mine, albeit wood instead of aluminium.
I use a 3 HP two stroke motor and find a different tie down works well.
On my TI, there are 2 U shaped lugs in front and two behind the outboard frame.
I simply tie 4 cords from the lugs onto the posts which as you can see stick out further than your dowels.
It probably takes a little longer to tie off the cords but it has the advantage of no drag from a strap under the hull. I have been using it like this for a couple of years without a problem with a heavier motor than yours.
Just a thought.
Don't the red ones go fast
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Cheers, Brian in South Australia
Tandem Island -