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Old 06 March 2013, 00:13   #21
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I'm keen to see how this turns out.

We used to have a 1980 Zodiac MkIIIGR, which had a short shaft transom. It would cavitate (ventilate?) all the time with our short shaft 35 hp Evinrude. When we upgraded to a 55 hp short shaft Evinrude Heavy Duty (a much heavier engine - 215 lbs vs 135 lbs if I'm not mistaken), the cavitation (ventilation?) problem went away - completely.

That's a beautiful boat, btw. I love it.
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Old 06 March 2013, 00:29   #22
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Originally Posted by Projectile View Post
I'm keen to see how this turns out.

We used to have a 1980 Zodiac MkIIIGR, which had a short shaft transom. It would cavitate (ventilate?) all the time with our short shaft 35 hp Evinrude. When we upgraded to a 55 hp short shaft Evinrude Heavy Duty (a much heavier engine - 215 lbs vs 135 lbs if I'm not mistaken), the cavitation (ventilation?) problem went away - completely.

That's a beautiful boat, btw. I love it.
Very Interesting! Sounds like I wouldn't need to worry about the extra weight of a 65 hp ETEC or a Yamaha F70 over my current Yamaha 40 hp 2 stroke.
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Old 31 July 2013, 17:44   #23
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No obstructions in front of the leg or prop, the boat has "high jackers / speed tubes / high risers' below the main tube and the cav plate sits inline with the bottom of the speed tubes.
It's a difficult situation to be in, as the boat starts to plane it also starts to bow steer, so I trim a bit and then it cavitates.
The prop is cupped (I don't have the size at the moment) and is a stainless steel one.
I can get the boat up on the plane quickly but it goes to crap there after!
I will check the pitch tomorrow (it's at a mates place).
I really appreciate your input everyone..
Troy,

How did this turn out? I'm having the same issue with my new Zodiac WB 465 with ETEC 30. The boat and motor are both long shaft. It planes easily, but as I accelerate beyond a slow plane, the bow digs in, I get a lot of spray coming off the sides of the boat, and its impossible to keep the boat straight. The floorboards creak a lot and the bow boards flex. As soon as I let off the throttle and go back to a slow plane, the bow comes up and everything relaxes and feels normal again. Trimming the engine up from the first to the third trim holes helps a bit, and when I reach trim holes 4 & 5, it cavitates (ventilates?). The boat and keel are all at max pressure, and it does this with the boat empty or my family of 4 in it in a variety of positions for weight distribution, so those are definitely not the issue.

My cavitation plate is 3 inches below the bottom of the transom, but may be level with the bottom of the keel, since the hull has a bit of a Vee to it by virtue of the inflatable keel. I have been advised to try raising the motor ...
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Old 01 August 2013, 22:33   #24
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Troy,

The floorboards creak a lot and the bow boards flex.
That should not be happening, and would suggest that you are under inflated. Perhaps you need to test the accuracy of your gauge.
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Old 01 August 2013, 23:46   #25
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That should not be happening, and would suggest that you are under inflated. Perhaps you need to test the accuracy of your gauge.
Thanks, but I have over 30 yrs of experience with heavy duty Zodiac inflatables. If there is one thing I am sure of, it is that the boat is well inflated. While I have checked with a gauge, there is little need to do so. I know that when I can't pump anymore in, it's over inflated, and I've been there with this boat when gauges confirmed over inflation. Problem persisted.
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Old 02 August 2013, 04:25   #26
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I'm suspecting that your out outboard is mounted about 2"-3" lower than ideal. I'd try incrementally raising the height by an inch at a time and see how it goes.
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Old 02 August 2013, 07:36   #27
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Its been my experience that when you can't pump any more with the foot pump you are at the correct inflation pressure.
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Old 02 August 2013, 10:29   #28
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Its been my experience that when you can't pump any more with the foot pump you are at the correct inflation pressure.
That's relative. Not all boaters weights or inflates same, heavy weights much better, skinny less and newbies worst. On some foot pumps valve connector pops out when correct pressure has been achieved, not on the ones having bayonet type end connectors though. Find hand pumps are much better and friendlier to inflate than foot pumps.

That's why is mandatory to monitor your final "assumed" perfect inflation with a pressure gauge, as most of the time will be under inflated...

Happy Boating
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Old 02 August 2013, 11:25   #29
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My cavitation plate is 3 inches below the bottom of the transom, but may be level with the bottom of the keel, since the hull has a bit of a Vee to it by virtue of the inflatable keel. I have been advised to try raising the motor ...
A picture from the rear would be good.
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Old 03 August 2013, 12:54   #30
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As requested.
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