Cav plate height for Zodiac Mk4 - Page 8

captnjack · 15 October 2013, 20:28

Engine height looks fine to me. Glad that question is resolved.

I would look very carefully at the manual and reassemble the boat though. The floor boards look too low in the latest pic (relative to the elephant trunk hole) but I've never had one of these hulls before, just a somewhat similar Bombard hull. In that construction there's a groove in the aftmost edge of the floor board, that groove fits onto the rib of aluminum on the transom, not above or below it, right onto it. But the manual is your best guid to proper floor board placement. Don't assume, just check the manual and reassemble step by step.

I have found foot pumps completely inadequate for getting proper tube pressure. Get a good pump (electric) and a good gauge and pump that keel tube to exact rated pressure. (although I use a scuba tank with adapter) If its underinflated you will end up with a "cupped" hull and the exact bow steering symptoms you describe.

The OPV on the foot pump could very well be defective or venting too soon and you'll never get a good ride with inadequate keel tube pressure. Readjust all the tube prssures after its been in the water at least 15mins.

Projectile · 15 October 2013, 20:50

The floorboards are appropriately assembled in the photo in my basement and the most recent one where the transom has been raised. The proper assembly is described on p.8 of the attached manual. The diagram indicates that one ought to expect to see the metal rim of the ledge on the bottom of the transom that fits into the groove of the rear floorboard. That rim ought to be visible just above the back end of floorboard at the junction with the transom. That's not the issue at present. However, in the spring, I do intend to reassemble the boat because I want to see what the aft portion of he keel looks like under the floor.

The large drain hole you can see in the recent pic is for rapidly draining deep water that is above the floor. There is a separate drain for draining water below the floor.

The manual indicates a goal pressure of 2.5 PSI. I had the boat pumped up to over 3.5 PSI and did so after the boat had 15 minutes to sit in the cold water. F*%ck these boats if one needs an electric pump to get proper pressure. I've been assembling and enjoying Zodiacs for over 30 years without an electric pump. Even as a 16 year old kid, I could over inflate a boat by jumping on the pump. In those days, Zodiacs had intercommunicating valves and you could screw on the gauge until it made an airtight seal with the valve. Those readings were pretty accurate and we must have had several of those gauges because we had several boats and they'd correlate well with each other. I never had a boat that put its nose down like this one. I know all about appropriate air pressure, and so I appreciate your advice to pay attention to it. Believe me, I do and on the day of the sea trial, I paid specific attention to the pressure including (and especially) the keel pressure. I really don't think that that is the issue. If it was, all kinds of people would be having serious boating issues (like I'm having) all of the time all around the world with inflatable boats. There's more going on with my boat than under-inflation of the keel.

captnjack · 15 October 2013, 21:00

Floor boards assemble exactly like my old Bombard (also made by Zodiac). Guess they just drilled the elephant trunk hole a little high.

2.5 psi for a keel tube sounds underinflated to me, but I've never had a boat with an inflatable keel. I'm starting to come around to Sibrider's position. Maybe the prop is radically off and entraining too much air leading to your annoying ventilation once you trim up the engine.

Ps My foot pump is only used in emergencies, it sucks humping that thing like a dog for 30 miutes to inflate a boat!

frankc · 16 October 2013, 02:02

Everyone is concerned that he had sufficient pressure at 3.5 lb when the manual states a target pressure of 2.5 lb. really? Does anyone doubt the ability of Zodiac to state a proper pressure.

Looked up my Avon manual which states keel pressure of 2.0 to 3.0 lb and 2.5 recommended, so that pretty well agrees with Zodiac.

The floorboard fits a tongue and groove piece, so why would anyone doubt he assembled the boat correctly?

Projectile, I will leave you to the experts, and I hope you get a satisfactory fix for your problem.

Projectile · 16 October 2013, 20:18

Quote:

Originally Posted by 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.

That's a really wonderful and generous offer, but I'm east of BC. Thanks, though.

Projectile · 16 October 2013, 20:24

Quote:

Originally Posted by frankc

Projectile, I will leave you to the experts, and I hope you get a satisfactory fix for your problem.

Thanks, frankc. You were the first person to bring a hooked hull to my attention and for that, I thank you too. I do believe that the behavior of my boat suggests a hull problem, and when I looked, sure enough, there was what appears to be a hook in my hull. This hypothesis has the most going for it right now.

I'll update the thread when I hear back from Zodiac, who are examining the pics.

SIBRider · 16 October 2013, 20:39

interesting that they reduced required air pressure so significantly. Love those original intercommunicating valves. F470 calls for 3.4 PSI main tubes and ~3.1 for keel.

Genius of design although bit more leaky maybe.

Projectile · 16 October 2013, 20:40

As this pic shows, the black stopper on the yellow part of the Bravo 9 pump will pop off at 4.4 PSI.

This confirms that my Zodiac dealer rep over-inflated the keel to 4.4 PSI as the over pressure stopper did pop off when he did so. IMO, this indicates *nothing whatsoever* about the pressure in the keel prior to the 4 or 5 pumps that he put into it. I had confirmed a pressure of at least 3.5 PSI after the boat had cooled off in the water for 15 minutes, and that's already 1 PSI greater than the recommended pressure of 2.5 PSI by the manufacturer. I provided objective evidence that my keel was properly inflated. My Zodiac dealer rep provided no objective evidence whatsoever that my keel was under inflated.

Accordingly, it is highly implausible to me that my keel was under inflated.

Projectile · 16 October 2013, 20:41

SIBRider, I too LOVE the intercommunicating valves. Our older Zodiacs from the 1980s all had those.

The FC470 is my dream boat. Enjoy yours in health!

It is interesting that they recommend a lower pressure for the keel than for the buoyancy tubes ... Since I aimed for the same pressure, I think it is even less likely that my keel was under-inflated. Remember, my Zodiac dealer rep indicated that he thought that my buoyancy tubes were appropriately pumped up ...

Projectile · 16 October 2013, 20:45

Quote:

Originally Posted by frankc

Everyone is concerned that he had sufficient pressure at 3.5 lb when the manual states a target pressure of 2.5 lb. really? Does anyone doubt the ability of Zodiac to state a proper pressure.

Looked up my Avon manual which states keel pressure of 2.0 to 3.0 lb and 2.5 recommended, so that pretty well agrees with Zodiac.

It is noteworthy that my boat, though badged as a Zodiac, is in fact, an AVON! AVON originally made the WB465 and still makes them in their UK factory for Zodiac. Now, they are black instead of grey, and the have Zodiac carrying handles and badges on them, but otherwise, same boat.

SIBRider · 16 October 2013, 20:56

they been together for awhile. Haven't they?
Does you keel extent all the way to transom? Could it be incorrectly positioned. I it removable? You should be able to feel it when inflated. If they managed to assemble something incorrectly once that may/will happen again.

Lay a 2x4 on floor. check how streight it is.

Northern Pike · 17 October 2013, 14:59

The working pressure should be stamped on the hull identification plate.
My PVC Futura says 3.4 psi.
Projectile, is your boat PVC or Hypalon?

And BTW, check your throttle linkage to be sure its opening all the way.
i went through several props wondering why my brand new motor wouldn't perform as I expected it to. Turns out my throttle linkage was incorrectly adjusted and was not fully opening.

Projectile · 19 October 2013, 00:46

Quote:

Originally Posted by Northern Pike

The working pressure should be stamped on the hull identification plate.

Seems that mine says 3.0 PSI. I don't know why the manual from Zodiac would say 2.5 PSI.

Either way, I aimed for 3.5 PSI after giving the boat 15 minutes to cool in the water, so the idea that my keel was under inflated remains implausible to me.

Projectile · 21 October 2013, 02:09

Here's what a hook in the hull can do, and a description of what I experience, too:

"The boat bow steers, quite severe in calm water, not so bad in a chop, white knuckle in following seas. Deadrise at transom is 22, at bow 56. Trimming out drives has no effect on trim, they will trim until props break free with no lift in bow."

This quote is from the link below, where photos of the hook in the hull are available. I'd say that they look similar to mine...

Bow steering help - Boat Design Forums

SIBRider · 21 October 2013, 18:45

I understand your concerns with hook but I doubt that it is that much on an issue. On rigid hull boats not doubt soft floor inflatables...? What speeds are we talking about here? Unlike picture above where entire hull is compromised. Large chunk of planing surface is formed by tubes themselves. Unless they have incorrect shape I doubt relatively small cup at end of keel can have such dramatic effect.

Can you clarify boat/prop behavior after raiser been installed and motor placed at neutral trip position (3 hole at least?). I remember adding small wooden block didn't help but raiser is much higher. Did you try to run with 3 hole trim and riser? What happened? Any video of that?

Projectile · 21 October 2013, 20:43

"Large chunk of planing surface is formed by tubes themselves."

In response to this, I have say, "So what?"

Trim tabs create a hook, and the trim tab doesn't have to extend all the way across the back of the boat from port to starboard to have that effect, so I have no problem seeing how a hook that is primarily in the centre of where the fabric meets the bottom of the transom and that is at least 12 inches wide can't do exactly the same thing as a trim tab.

"Can you clarify boat/prop behavior after raiser been installed and motor placed at neutral trip position (3 hole at least?)."

Constant cavitation/ventilation as soon as the boat is planing and the bow down attitude is not eliminated. Before the engine was raised, when A/V plate was 3 inches below the bottom of the transom, I could trim out to 3rd hole without cavitation/ventilation and the boat would still bow-steer like crazy as I accelerated from planing speed. Back then. I had to trim out to 4th or 5th hole to get cavitation/ventilation, and even then, the boat would bow steer with acceleration from planing speed.

With the engine raised to "proper" height, I can only avoid cavitation in trim positions 1 or 2 closest to transom (inward most). Beyond that and cavitation/ventilation becomes unacceptable and bow is still too far down (though the bow down attitude is better than when the engine was sitting over 2 inches lower).

captnjack · 21 October 2013, 21:06

No amount of screwing with the engine height or trim, or with the prop size or pitch is going to solve a fundemental problem with the hull.

I think you need to go roll up your SIB and take a road trip to another dealer who has a clue. Go look at another hull, both how the floorboards are setup and how taut the floor material is. Compare with your own and try to come up with a solution.

Projectile · 21 October 2013, 21:27

I agree CapnJack. Unfortunately, this'll all have to wait for spring at this point. I am, however, dying to know right now. Oh well.

My dealer and Zodiac have been good so far. We have a sea trial reservation this spring.

captnjack · 21 October 2013, 23:27

Ahh bummer
I forget most of Canada is frozen or freezing over now.

SIBRider · 21 October 2013, 23:57

Time to head south for vacation!
Anyway. One thing that caught my eye before is location of your self bailer.

Logically I would place its bottom edge at least inline with floor otherwise you boat will have standing water after getting swamped since not all of it will drain out. That's the way my F470 is (Let alone there is one below floor) It's inline.
Of few pictures I could find on net.

2005 Avon W465 | Boats & Yachts for sale | Used Boats and New Boats for sale

http://zodiacmilpro.com/wp-content/u...B-range-IT.pdf
Bailer opening appears more or less inline to floor.
If that rear retainer is too low floor will be out of parallel with tube's axis. I think that could cause tubes to take inverted hook sorta banana shape as they conform to rigid stringers. As result engine might be running too high in relation to keel line hence cavitation/ventilation or I suppose result maybe unpredictable. Maybe front will come down a bit since front panels don't have any rigid stringers connecting them.

I would lay a board across tubes and measure distance to floor at different points. See if they are parallel. And/or flip boat over to check for straightness.

Ask defender to send you picture of another work boat. Amazingly hard to find this stuff.