Sunday, May 13, 2012

Cockpit and Motor Mount Measurements and Details

A reader and fellow Tiki 26 builder wrote the other day to request some measurements on my cockpit clearance above the waterline and the depth of the prop of the Nissan Extra-Long Shaft 6hp outboard.  Because the cockpit is slightly deeper than the 9 inches shown on the plans, he was concerned about wave tops slamming the bottom, and also wanted to make sure the prop was deep enough to avoid cavitation in a chop.  I had to reinstall the cockpit the other day to make some other measurements anyway, so I shot these photos showing the requested dimensions.  I made up for the two-inch extra cockpit depth somewhat by making my beam mounting blocks on the deck thicker by almost that amount.   I don't think clearance will be an issue, and with the extra-long 25-inch shaft, the motor can be mounted high in the cockpit to protect it, yet it will still reach deep enough so that it will almost touch bottom if the keels of the hulls do.  This first shot shows the depth of the cockpit hanging below the aft crossbeam:

Here you can see can see the depth of the prop, again measured from the bottom of the aft crossbeam:

The bottom edge of this piece of 2 x 4 lumber is in line with the bottoms of the keels adjacent to the motor.  As you can see, the prop can't hit bottom before the boat runs aground, as the deepest part of the keels are slightly forward anyway, in the midships portion of the hulls:

This last shot shows the 2 x 4 at the approximate average load waterline.  The bottom paint is probably 3-inches above the true waterline to allow for heavy loading at the start of a voyage.  As you can see, with the extra-long shaft, the prop is unlikely to come out of the water in anything but the worst conditions:

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