Cavitation on Zodiac

[bdemaso]

Recently purchased a Mark 3 15'5" Zodiac inflatable. Have 25 hp Merc. Had motor on a 11'2" Seaworthy inflatable that would occasionally spin out (cavitate) when in rougher water. Seaworthy had a mimimal keel. Zodiac has a significant keel giving a more v-hull effect. Had the Zodiac on the lake for the first time prior to upcoming ocean trip this weekend and it would cavitate all the time. Could never really get much of a high end speed before it would spin. The transom height is 15" and the front of cavitation plate is level with the bottom with the back of the plate raising 1/2 inch. The former owner had drilled 4 holes in the cav plate and had installed a foil type device that slows the boat speed down for troling. Removed the foil but 4 hole remain? The angle of the motor is the the 2nd hole closest to the transom. Any thoughts or suggestion to my problem?

 

[crazy charlie]

Re: Cavitation on Zodiac

Sounds like you need to change the prop to accomodate for the larger heavier boat.Can you get any weight into the bow to assist you in planing.Did you use the boat with and without the foil.I would guess the foil would help.Charlie

 

[jheron]

Re: Cavitation on Zodiac

You can try adjusting the angle of the motor I would try and move it closer to the transom thus getting more of the lower unit in the water at plane. I have a 10' zodiac with a 9.8 on it and I tried one of those foils you describe but it would lift the motor rite out of the water and cavitate every time I hit the throttle I had to remove it rite away that was 2 years ago and the holes are still empty and I have no problems.<br />regards Jon

 

[Snowdrggn]

Re: Cavitation on Zodiac

I have a 10ft Zodiac with a 15hp Evinrude on it. the OEM prop (9.5x10p) had lots of cavitation/ventilation issues. I switched to a Pirhana prop (10x11p) and it settled down a lot. Also I mounted a set of Smart Tabs on it and they made an incredible difference as far as holeshot and the time it takes to get on a plane (about 1/3). It just kind of gives a little "grunt" and it's up and gone!

Just my 2 cents......

 

[Snowdrggn]

Re: Cavitation on Zodiac

Just an update, I sold my zodiac and replaced it with a Zebec ( 10 ft) which is a wider heavier boat. Initially I had cavitation issues, but after installing Smart Tabs, and modifying a Pirhanna prop, it seemed to settle in okay. The boat being heavier than the Zodiac was, has quite a bit lower top speed though.....

Here is a short clip of it on the water.

http://smg.photobucket.com/albums/v48/Snowdrggn/Zebec/?action=view&current=DSCF0021.flv


Cheers,
Snow.

 

[Vlads Quiff]

Re: Cavitation on Zodiac

Hi Snowdrggn, I have a 10 foot Zodiac and I am told that a 10hp is the biggest engine that can be fitted, is it OK to go up to a 15hp?

regards VQ

 

[Snowdrggn]

Re: Cavitation on Zodiac

Vlads,
I'm not going to advocate overpowering anything in a public forum. But let's take a look at a few things.
the 1974-1995 9.9 and 15 hp Johnrudes both weigh in at 72lbs. for the short shaft, manual start model. The 15 makes its extra power by having a higher wot rpm. The hole shot is not noticable stronger (almost seems a tad weaker) from the 15hp, the weight is the same, so what really are the added stresses? I feel a 120 lb 10 hp would create bigger issues, than a 72lb 15hp on a small inflatable boat. Locally there are a couple of Zodiac Cadet 310s with older 20 hp Mercury engines on them. (Heavy!) that have run without incident. As long as the "Stupid Factor" remains under control, I have witnessed no bad effects. I have had a 25hp Erude on my boat and it seem to handle it okay, but is a bit heavy (125lbs). the 25hp Yamaha @ 104lbs seems like an ideal test subject next......... Hmmmmm....

As far as the legal or insurance side of it goes, you're on your own.

Cheers,
Snow.

 

[Vlads Quiff]

Re: Cavitation on Zodiac

Cheers Snow
As it happens I have a 1992 8hp two stroke 'rude on mine. I hear what you are saying about insurance etc, but you feel that a motor of similar weight up to around 15hp should be OK?

regards Vlad

 

[Snowdrggn]

Re: Cavitation on Zodiac

Vlads,
When I first got my 310 Zodiac, I had a 1986 8hp
Evinrude on it. It didn't like to climb out of the water with 2 people in it, but would go okay once it got on a plane.
A 9.9 or 15 woke it right up though. The extra torque made all the difference to it, as well as a set of smart tabs. If you check the link to the picture you will notice that the boat is just coming onto a plane, the hollow in the water behind it is where I twisted the throttly from a standing start........

http://img.photobucket.com/albums/v48/Snowdrggn/Zodiac/Dscf0051.jpg


Cheers,
Snow.

 

[Vlads Quiff]

Re: Cavitation on Zodiac

Hi Snow
Yes have just had a look around deffo gives mine as 10hp.
As you say for example the mk 1 futura is a foot longer than mine and has a 30hp capacity, obviously the make up of the boat is different, but that much different.
I think I will upgrade to a 15hp four stroke, when funds allow.
thanks
Vlad

 

[Snowdrggn]

Re: Cavitation on Zodiac

Me Bad!!!!

Sorry I got posters mixed up!!!

Vlad,
4 strokes can be quite a bit heavier than 2 strokes.
The lightest 4 stroke I'v found around here is the new Honda 15/20hp (same weight for both) at 101lbs. My 15hp Johnrude is 72lbs. Is there any chance the manufacturer of dealer could let you know the maximum motor weight for the boat? I know some of the more inexpensive brands of boats have smaller tubes and lower payload capacities. I also would be cautious with overpowering a boat of unproven durability history ( eg: tortured by others!) I honestly feel that the power gain of a 15hp 4 stroke may be negated by the increase in weight over a 10hp 2 stroke. Personally, I would search out a Johnrude 2 stroke, as they are one of the lightest and reliable engines around.

Did you check the link to the video I posted? That is a 130lb boat with a 15hp JohnRude and smart tabs fitted.

Cheers,
Snow.