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Old 19 January 2014, 18:27   #1
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Country: Australia
Town: Australia
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Make: JP Marine 3.8 Patrol
Length: 3m +
Engine: Tohatsu 18hp 2stroke
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Posts: 69
Motor Height Question

Hello Sibbers

I have a 3.8 m JP Inflatable SIB with a 18 hp sshaft Tohatsu and 9"prop. I use this boat for spearfishing in the ocean (swells and wind chop). The boat carries two divers 110 kg (me) and 80 kg (son).

I was getting a fair bit of water spraying into the back of the boat when I first installed the motor directly on the transom. So I experimented with a number of engine heights. Then got an aluminium bracket made up that slips over the transom without having to drill holes. See the attached photo.

I consider the spraying problem to be fixed. Ie when travelling in a straight line and motor thrust rod in the hole closest to the transom. However, I get a little bit of cavitation when travelling in a straight line if I move the thrust rod out one hole.

Am I being anal or should I get another bracket made up to lower the motor about 5-10 mm or else buy a mini jacking plate.

What are your thoughts?
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Old 20 January 2014, 02:00   #2
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Boat name: Uh...a kayak?
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Could you post a photo from behind showing the lower leg of the outboard, and the bottom of the boat?
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Old 20 January 2014, 06:00   #3
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Country: Australia
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Make: JP Marine 3.8 Patrol
Length: 3m +
Engine: Tohatsu 18hp 2stroke
Join Date: May 2013
Posts: 69
Hello Peter. Attached are 3 photos showing the lower leg of the outboard. Note that the cavitation plate (top of the straight edge) is approx 40 mm below the bottom of the transom at the centreline. Sorry for the poor quality photos, it is night time here now.
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Old 20 January 2014, 11:24   #4
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Country: Other
Town: Lima-Peru
Boat name: Nautile
Make: Sea Rider Boats
Length: 4m +
Engine: Tohatsu 18 /30 HP
Join Date: Sep 2007
Posts: 1,706
If you have time to fully read this thread and follow to the line recommendations be my guest...

ABC Sib-Rib Installation Guidelines.-*/ 628902


Happy Boating
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