Weird! Zodiac arches it back then cavitates

[Peter_C]

I have put a few hours on my new to me Zodiac which is a MKII HD.



It was all going good until we hit this problem.



Then it started doing something I have never felt before. Of course it is the first time I have driven it fully loaded on glassy water. When running full throttle at 23.4 mph or so, what it does is arch it's back so to speak, then unloads picking the transom up out of the water a little. This causes the motor to cavitate for a second. Then it starts the process all over again and releases about 20 seconds or so later. If I slow down to around 19 mph or thereabouts it does not do this. We tried moving people around both forwards and backwards with no results. It seems like it is an air pocket forming or something. Not really an issue since the Pacific Ocean is never dead flat, and diving a lake is something we will not be doing anytime soon.

Anyone else experienced this?

[John Kennett]

Hi Peter

You've posted links to some pictures on scubaboard.com but they won't show here. You will need to upload them as attachments.

[Bigmuz7]

I have , although not in that particular boat, shifting weight usually sorts it for me, so I can get the bow up a bit, make sure your engine trim stop, isnt set too low if it has one, and also that your tubes are at the right pressure, of even if you think they are, try making them a little firmer to see if it helps

[prairie tuber]

How many psi are you inflating the main tubes and the keel to?

[matt h]

if the driver and passengers would sit right in the middle, the problem would go away,

the keel is not deep enough, try it

[1ThOFA87]

I have the same problem. Mostly when I have my brother aboard. He's pushin' close to 400 lbs and I've had him sit about mid front center and mid starboard. I'm 200 pounds so he's double my weight and I can't find anyplace to sit hiim without this problem. I'm going to get an electric pump and see if it gets my tubes firmer than I can with my foot pump.

[prairie tuber]

Just in case I hadn't asked earlier;

How many psi are you inflating the main tubes and the keel to?

[1ThOFA87]

Originally Posted by prairie tuber

Just in case I hadn't asked earlier;

How many psi are you inflating the main tubes and the keel to?

I don't know about Peter but I have no idea about mine. I have a footpump and fill it until it won't take anymore air. What should they be inflated to?

[prairie tuber]

Main sponsons should be 3.4 psi, the keel just a bit higher. I would highly recommend getting a guage, proper inflation pressure is critical to the performance of the boat.

[Peter_C]

LOL I forgot I posted this thread.

I keep the all of the tubes set at the spec written on the transom. My pump has a gauge on it, although it is cheesy.

Over the new years holiday it actually did cavitate on the Pacific Ocean because it was glassy flat inside Monterey Bay. Again we tried moving people around to no avail. I plan to buy a really nice gauge to make sure I am pumping to the proper pressures.

Also found out with four divers and six scuba tanks onboard, the boat takes awhile to plane.