Cav plate height for Zodiac Mk4

[Projectile]

Originally Posted by SIBRider

then again even judging by tiller handle angel. Yours point up theirs just about level. Your motor is significantly more trimmed-in then theirs.

Tiller handle angle is fully adjustable on my engine and I like it up a bit. The engine was not trimmed in to the first trim hole when this pic was taken as it was when the Zodiac rep was driving.

However, you are right SIBRider, that the bow down attitude my boat has compared to the Zodiac advert may be contributed to by different engine trim. I just can't make the bow down attitude seen in the pic of my boat go away by trimming out, plus I get crazy cavitation when I do.

[Northern Pike]

Cavitation and ventilation are different.
If when you trim out you get ventilation, then your motor is too high.
If it is indeed cavitation, then it could be as others have noted, due to the hull shape.
That hook does look rather severe, and may well be the cause of your problems.
Return shipping across the border could be a hassle, but you may have a defective boat on your hands.
See what Zodiac Canada will do for you.
And let us know.

[captnjack]

Projectile where are you in Canada? Anywhere in BC? I'm kinda out of commission right now for boating, but in a few weeks I'd be happy to take a ride in your SIB and offer some suggestions on what's going wrong. I'm in the Seattle area.

[SIBRider]

I'm not arguing whether there is a hook or not and how that affects performance. There is a stated concern that motor doesn't perform at correct trim angle. This problem is counteracted by position motor in manner that greatly exacerbates any possible hull problems. In fact it probably has far greater effect. Once good propulsion is established only after that I would be concerned with other issues. Motor that doesn't perform will not be able to raise bow. Hence it's pointless to fight other battles before this one is won.

[captnjack]

Originally Posted by SIBRider

I'm not arguing whether there is a hook or not and how that affects performance. There is a stated concern that motor doesn't perform at correct trim angle. This problem is counteracted by position motor in manner that greatly exacerbates any possible hull problems. In fact it probably has far greater effect. Once good propulsion is established only after that I would be concerned with other issues. Motor that doesn't perform will not be able to raise bow. Hence it's pointless to fight other battles before this one is won.

There's nothing that drastically wrong with the OP's prop. Even if its sized pretty far off the correct size, changing to a 4 blade or changing the pitch 2" is not the issue here. Those are minor tweeks to a major problem.

There are 2 possible sources to projectile's problem:
1) the shaft length on the engine is too short or its mounted way too high. Hence the only way to put the prop in the water is to trim it all the way down.
2) there's a huge cup in the hull.

Or both simultaneously.

I'd like to know the shaft length and see the motor mounted on the transom to rule out #1

[SIBRider]

Originally Posted by captnjack

There's nothing that drastically wrong with the OP's prop. Even if its sized pretty far off the correct size, changing to a 4 blade or changing the pitch 2" is not the issue here. Those are minor tweeks to a major problem.

There are 2 possible sources to projectile's problem:
1) the shaft length on the engine is too short or its mounted way too high. Hence the only way to put the prop in the water is to trim it all the way down.
2) there's a huge cup in the hull.

Or both simultaneously.

I'd like to know the shaft length and see the motor mounted on the transom to rule out #1

While it may seem so. I had significant performance problems with stock prop similar to what Projectile describes that went away changing to 13" prop and/or upping motor. Most of those stem from undersized prop (because of undersized motor) that has to operate at greater slip.

[captnjack]

I have lost track of Projectile's horsepower and prop dimensions. I thought it was 25hp which should be close enough with the default/stock prop supplied.

[SIBRider]

etec-30 stock 10x12x3 I believe. Which is not too bad you would thinki but problems he describes are so similar mine... I

[captnjack]

Originally Posted by SIBRider

etec-30 stock 10x12x3 I believe. Which is not too bad you would thinki but problems he describes are so similar mine... I

Shaft length and transom height?

[SIBRider]

You can see his original setup here at the bottom before they added raiser. http://www.rib.net/forum/f50/cav-pla...4-53656-3.html
18" transom 20" (actual 21.5) shaft.

[SIBRider]

Reading this though

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, ...

indicates running with engine trimmed in and hull exposed to lot of stress from motor trying to cave it in. Makes me wonder now if some permanent damage (bending) occurred to stringers, floorboars etc. Or possibly transom mounts.

[Projectile]

It's a long thread with other people's issues mixed in, so I can see how it's hard to follow everything. Thanks for hanging in there everybody.

The shaft length measures 22 inches and the transom height measured 19 inches. Both are called "long shaft" by the manufacturer. The prop is the standard prop for a 2013 ETEC 30 and it says 10.3x12 on it.

The first pic is of the AV/plate in relation to the bottom of the transom initially. As you can see, the A/V plate was 3 inches below the bottom of the transom (as one would expect with a shaft of 22 inches and a transom of 19 inches). At that time, the boat would plane very easily and as I accelerated, I had much worse bow down attitude compared to now (I couldn't even get to wide open throttle because as I accelerated there was serious bow steer and stress on the boat). There was no cavitation unless I trimmed out to 3rd trim hole and became virtually constant at the 4th or 5th trim hole. Trimming out made it considerably harder to get on plane and helped a bit with the bow down attitude as I accelerated, but it was still extremely problematic. I spent most of my time boating on my vacation at half throttle and with the engine trimmed up to the second or third trim hole.

The second pic shows the motor raised with a block of wood 3/4 inch. This made little difference.

The third pic shows the transom built up as performed by my dealer. I was told that this should solve the problem.

The 4th pic is of the A/V plate in relation to the bottom of the transom with the motor sitting up on the raised transom. The A/V plate is about 1/2-3/4 inch below bottom of transom. Dealer told me that this is perfect height. As described above, the bow down attitude is better now (at least I can get up to WOT) but still problematic. However, now, when I trim out to try to get the bow up, I get plenty of cavitation. I get it even trimmed all the way in or in the second trim hole (it didn't do this before it was raised), though this was virtually eliminated when the Zodiac rep got in the boat with me and I figured that this was simply due to our combined weight in the boat. The boat was otherwise empty (life jackets). I weigh 160 lbs and he admitted to weighing over 200 lbs (240 lbs I think he said?). The bow down attitude was still present, however. I was told that the bow down attitude was normal, but I find that hard to believe.

At no point did trimming the motor out resolve the bow down attitude with acceleration.

I was told that the boat was underpowered despite the fact that Zodiac recommends 25-40 hp and I have a 30 hp engine. I was told that if I upgrade to a 50 hp motor, the bow will come up. I find that hard to believe because the bow sits just fine when I get onto a plane. It is when I accelerate and apply power that the bow gets pushed down. The more I accelerate, the more it gets pushed down. I don't see how *even more* hp is going to make that better. When I explained the difficulty I was having accepting that the bow down attitude was due to the boat being underpowered, I was told that "it is hard to explain".

The guys at my Zodiac dealer are nice and good guys and they have been very willing to help me out even though I didn't buy the boat from them. That says something. Zodiac has been very supportive and has covered the cost of the transom raise by my dealer. I'm open to the possibility that the boat is underpowered, despite finding it implausible. We plan to go for a test drive in the spring with a 50 hp Yamaha.

[Projectile]

There is one more thing that I should add for full disclosure.

At the last sea trial, I launched the boat, walked it over to a dock, and then parked my truck. The boat got to sit in the water for a good 10-15 minutes and cool off before I got back to it. I then proceeded to pump up all 5 air compartments and the keel by jumping on the pump until I could get no more air in. The over pressure stopper on the pump blew out while pumping up several of the compartments. The gauge read well over 3.5 psi. on all of them.
When my Zodiac rep arrived, I asked him if he thought the boat was appropriately pumped up and he checked it and said that he thought that it was. The keel was pumped up as hard as the buoyancy tubes at that point and he thought that the buoyancy tubes were just fine.

I went for a ride by myself and it cavitated like crazy, even trimmed all the way in (down). He went for a ride and it cavitated with just him in it too. The bow would still come down as shown in the video and photo with acceleration. Remember – I was told that this is normal.

When we got in the boat together, as if magically, the cavitation got considerably better. Travelling downwind, the boat would cavitate on turns, and travelling upwind, it hardly cavitated at all. We got back to the dock and my Zodiac rep checked the keel and he said it felt a bit soft. He proceeded to put 4 or 5 pumps of air into the keel and he was able to do that because he weighs more than I do. On the last pump, the over pressure stopper on the pump blew out and he said that that is how you know that it is appropriately pumped up. We went out for another ride together and there was no cavitation at all in the second trim hole up. Bow was still down with acceleration, however.

He interpreted the cavitation being due to an underinflated keel. However, the cavitation was eliminated when we drove the boat together prior to adding air to the keel. I interpret this as the keel being adequately inflated, and then over-inflated. There was no objective gauge reading before he added air to the keel and the rep said that the gauges are “useless anyways”. Either way, the bow-down attitude was still present.

I’m prepared to accept that there may be a slight issue regarding keel pressure and cavitation, but I think that the problems I had with cavitation are due to more than that. The big difference occurred when there was more weight in the boat and before any air was added to the keel. Finally, I don’t think that the keel pressure has anything to do with the bow-down attitude of the boat.

[SIBRider]

Something to note. Pic #3 shows floorboard considerably below drain hole. Yet on page 4 http://www.rib.net/forum/f50/cav-pla...4-53656-4.html
it's almost level and retaining plate is not visible. Was something modified or you floor flexes in and out that would indicate like someone mentioned before shorter then normal floor. what does your front look like. Do you have thrust board upfront? Does it look ok? Is there any provisions to drain water from under floor boards? F470 has a drain right by lowest point on transom. Could offset balance I suppose if not.

[Projectile]

That's an interesting observation SIBRider. I hadn't noticed that before.

There is a groove at the back edge of the rear floorboard that fits over a metallic "ledge" at the bottom of the transom.

My dealer assembled the boat at the start of the season positioning the rear floorboard as you see in the pic on page 4 of the thread.

Pic #3 above shows the position of the rear floorboard after my dealer modified the transom to raise the motor. They assembled the boat at that time as well. I can't explain the difference, but presumably it has something to do with whatever modifications were made at the time. It looks like the floor is lower now (since transom modification).

I have never perceived the aluminum floorboards moving or flexing when underway. There is no thrust board in the WB465. There is a small drain low in the transom.

[SIBRider]

It should fit in not over. Like on later/current picture.

[Projectile]

Here's a pic after I assembled the boat in my basement when it first arrived (winter!). I specifically recall being careful to make sure that the rear floorboard groove fit that transom ledge, and you can see that the floor was in the lower position, as it is now.

Perhaps my dealer inappropriately assembled the boat at the beginning of the season and that rear floorboard was not in that groove, but rather, was sitting above it.

It was probably correctly assembled by my dealer after raising the transom, explaining why it is in the lower position again now.

I'm not sure if or how that might have caused any problems, though ...

Might it have caused the hull material to stretch and form a cup?

[Projectile]

Originally Posted by SIBRider

It should fit in not over. Like on later/current picture.

Correct. That's what I meant. By "over", I didn't mean "above". By "over", I meant that the floorboard groove goes "onto" the ledge, the way that a cover may go "over" something when you are putting a cover "on".

We're on the same page.

[chipko]

Just an obversation but should the floorboard not fit below the aluminium angle fixed to transom. Looks like floor is sitting on top of said angle in photo.

Photo below of my zodiac transom (admittedly not the same model) where floor is located below timber batten on transom. This locks rear floor panel in place against pressure of keel when inflated.

[Projectile]

Originally Posted by chipko

Just an obversation but should the floorboard not fit below the aluminium angle fixed to transom. Looks like floor is sitting on top of said angle in photo.

Photo below of my zodiac transom (admittedly not the same model) where floor is located below timber batten on transom. This locks rear floor panel in place against pressure of keel when inflated.


Attachment 86437

No. I've had a couple of Zodiacs that were like yours. The WB465 has a different mechanism for the rear floorboard using a groove as I described.