Cav plate height for Zodiac Mk4 - Page 9

Projectile · 22 October 2013, 00:38

Thanks SIBRider. It may be that the large drain hole was drilled high, but I am certain that the floor is properly assembled in that picture; the rear floorboard is fitting "tongue in groove" with the ledge on the transom.

Hey, before you modified your transom to raise your motor, and your A/V plate was 2-3 inches below the bottom of the transom (as mine was before modifying the transom too), did you have severe bow steer at any trim angle, or just reduced performance and maybe some excess splashing?

SIBRider · 22 October 2013, 06:23

I meant that tongue-and-grove ledge is possibly mounted too low. I'd suspect it's fitted later in process after boat been glued together. Hole is most likely drilled in a jig or with CNC at the same time when transom is shaped.

I only run about for about a week before building riser. Performance was abysmal. Lots of splashes. I didn't do much WOT testing since motor was new. Mostly run with my entire family on board. I remember once taking it up to WOT briefly with just me. It was wild ride. She got to 20-21 mph then she wanted to go each and every way barely controllable.
Reason why I got into this thread was I felt that your problems described at page 3-4 seemed similar.

SIBRider · 22 October 2013, 06:25

Once on a plane boat rides pretty flat though even now.

The Gurnard · 22 October 2013, 17:40

Hi again Projectile

First...Im no expert on boat designs so take my words with a pinch of salt.

I do know my own inflatable boat pretty well though, so posted this to give some food for though with a view to try and help by comparisons, as there is obviously something wrong with your boat.. although I have no idea what ?

Earlier, some folks were suggesting pressure in the tubes and keel could be the problem. Im certainly not suggesting that is not the problem, but I know with my own inflatable ..it wouldn't be.

The reason I say that is... I like to keep a flabby SIB when its on land and even put it in the water that way.. as seen from this photo.

Then, when the boat is assembled with engine.. I clamber on board and pump it up with the hand pump. It is at the right pressure for me when I hit the tube with a clenched fist and it bounces off. I wouldn’t know a PSI from a metal bar ..so pressure in mine will vary depending in how hard I want to punch it on the day. Yet I still get a beautiful smooth wake with little turbulence from the prop part and with most turbulence streaming off the ends of the tubes as in this photo..no pressure gauge used...ever.

I also think that my wooden floor is designed to bend and flex at the section joints up at the bow end. I can tell this by the way the pieces slot together..one side is almost D shaped so it flexes or hinges in the slot on the other floor piece..if that makes sense. The whole bottom of my boat is also banana shaped..in a similar manner to your description of a hooked boat. Im pretty sure the bottom of my boat changes shape constantly as waves push and pull at the whole flexible bottom as I change speed or angle of attack to waves etc. But I dont have your problems.

I have a fish finder on my boat and keep my transducer on a DIY "slot" so I can slide the transducer up and down or even remove it to put it onto another boat. Im mentioning this..because when Im on the plane..if I slide that transducer even as little as 1/4 - 1/2 an inch too low ..I get a lovely rooser tail wake coming up from it.. it can easily reach the height of the transom. See photo of transducer and its sliding mount on my transom

Looking back at this photo you posted of the rear of your boat.. does that transom step not look very low compared to the rest of the bottom of your boat ? Almost as if it had slipped slightly when it was all glued together ? Could it act like the transducer on my boat when its a bit too low and throw up a rooster tail ..or if engine trimmed to combat it.. force the bow down and cause stearing problems ? I know my boat..although it is banana shaped underneath .. it does not have a pronounced step as shown in this photo of your boat.

Perhaps you could send that photo to the supplier you are dealing with..and ask them to send you a photo of another similar boats transom step ..to see if it is a problem on yours ? hey ... perhaps someone else who has the same boat as you and is reading this..could post a photo of their transom step..to eliminate my thoughts..

As mentioned at the start of this post..Im certainly no expert.. so take this posting as you will.. I do hope you get the problem resolved.

Locozodiac · 22 October 2013, 21:33

Gurnard,

The bow as shown on first picture, looks way under inflated, if you have invested so much money on that nice sib, do your Quicksilver a big favor, buy a pressure gauge. Using your fist to test your tube's pressure doesn't work as you expect. You will always be under inflated with fist check, worst when sib is floating on water after some time rest.-

If continue inflating and using that way expect transom ungluing issues shorty, worst scenario if boating heavily loaded and with max 4 strokes HP engine on choppy seas, jumping waves.-

Happy Boating

The Gurnard · 23 October 2013, 07:25

Many thanks for your concerns over a soft SIB Lucozodiac. As mentioned Im no expert and can only refer about my experiences with my inflatable boats.

I posted to show that my Quicksilver does not have bow steering problems, cavitation or water over the transom issues, even though.. as you appear to agree.. I probably run it under inflated. I think the Quicksilver has a similar type of bottom as the MK4 Zodiac ? so wondered if comparisons would help Projectile. I suspect he would be over the moon if his boat ran correctly..over or under pressurized.. then he could work that issue out.

While I appreciate that from a purist’s point of view .. trying to get maximum performance out of their SIB.. a pressure gauge is a must.. I do think there are lots of horror stories going around that if you don’t use one.. you will have bow steering issues, cavitation issues or worse still .. your transom will fall off. That is only my opinion though

The Quicksilver I now own and shown in the photos is a 2005 boat. It belonged to a friend before I swapped a hard shell boat for it. I admit that I have only had it since the summer and done around 500 miles...but my friend used it for diving for the rest of its life. I can assure you that a pressure gauge as been no where near it as the thump test suited him too. For an 8 year old boat with regular use.. I think it’s transom is as sound as the day she was made :-D

Perhaps it will fail a year or so before it would if a pressure gauge was used ..but I suspect that could be around the same time as the rest of the boat fails ? 10-15 years from a PVC boat is great value anyhoo..some fibre glass boats die of osmosis long before that L

I do respect your experience with boats Lucozodiac .. so what is your thoughts on the shape of Projectiles transom as shown in his photograph ? Do you see many like that and do they work as advertised ?

Northern Pike · 23 October 2013, 13:06

I agree with Loco's comments re. pressure gauge. Underinflation will ruin your boat and give you poor performance.
That pic of the hull and the wood makes me wonder if the inflatable keel was properly installed. It looks like it may have been folded over onto itself and not extending fully rearward to the transom.
Or it may be improperly installed in the hull by Avon, placed too far forward.
That wrinkly area of the hull should be taught and stretched downward and outward by the inflatable keel on the inside of the hull and under the floor.

The Gurnard · 23 October 2013, 16:34

Quote:

Originally Posted by Northern Pike

That wrinkly area of the hull should be taught and stretched downward and outward by the inflatable keel on the inside of the hull and under the floor.

Yup.. that ties in with my thoughts.. is there something not quite right in that area just before the transom. ?
I have taken a liberty and adjusted the contrast in Projectile,s photo so the area is clearer to see ..to me ... it looks quite wrinkly there and I know my transducer throws up a lot of water if its a tad too low and disrupts the main water flow below the boat.

For a comparison.. here is a better photo of the rear, underneath area of my Quicksilver. I should mention that it is in winter storage now and the inflatable keel has very little air in it. I have the top covers tied down so don’t want to disturb it all to blow the keel up.. but even with little air..its still very smooth at the rear end of my boat.

I don’t know what all this proves.. but I do wonder if that wrinkly area is the cause..
I think Projectile will have made sure it is assembled properly.. so perhaps the transom was set and glued in the wrong position during construction..if that could be possible ?

Anyhoo..there is little more that I can add to this thread.. its just thoughts.. so take my thoughts or leave them as you choose

Projectile · 24 October 2013, 03:13

The Gurnard,

Thanks for your concern and your comments.

Underinflation is like religion. You can always believe in it while you can never prove it.

I've indicated in this thread that I did use a gauge and got proper pressure even after letting the boat sit in the water for 15 minutes, and still there are skeptics here! Maybe my gauge doesn't work, they offer!

Underinflation is unscientific: it seems that you can never falsify the hypothesis that underinflation is the problem.

Well, I don't buy any into religions, and I don't buy that underinflation is the problem with my boat either.

Thanks again for your input.

SIBRider · 24 October 2013, 15:30

I'm certainly guilty of not re-inflating boat to spec pressure after temperature drop after sunset on occasion. My keel has a leak as well and gets soft after few hours. Returning home on somewhat flabby boat worst problems I've experienced was loosing 1-2 mph at the top. I'm sure floor shape at the time was far from perfect. No other ill effects such as bow steer or whatever.

Another data point though. Last weekend I took my boat out specifically to see how it will perform with my stock low pitch prop. I swapped for 13" prop and raised motor at the same time. Since all this discussion I decided to experiment. Mostly it was as expected: Easy to over-rev. Couldn't move past 2/3 of throttle once on plane. Good grip on 3rd hole. Bow steer at #2. #4 was biggest difference though. Intolerable cavitation/ventilation on anything but smooth straight line. Cresting even small wave it would loose grip over-rev instantly. Very different from 13" that I normally run. With later on 4th hole It feels at worst a bit loose but not much else. No over-revving, no major cavitation.

Projectile · 24 October 2013, 17:52

Thanks.

Can you tell me what the 2 prop descriptors are?

SIBRider · 24 October 2013, 18:10

OEM I believe is 10.25x10x3. 2.09 gear case. Other prop - Hustler 10.125x13x3. The later honestly is rather crude prop compared to OEM Suzuki IMHO. Just comparing thinkness, edging, finish etc. Motor feels smother with OEM as well. I've been thinking to ditch Hustler in favor of OEM 13" or matching stainless. I reach 5000+- some with 13 which is in mid-range of 4500-5500 WOT recommended for this motor right now. Should gain some RPM with better prop I expect. Rev limiter kicks in at 5500 sharp.

Projectile · 25 May 2015, 03:07

It's been a real saga, but I finally have my problems all figured out. Thanks to all who helped, especially frankc, captnjack, and SIBRider. Without them, the explanation would not be forthcoming.

The ENTIRE problem was cause by my local Zodiac dealer failing to properly assemble my boat after I brought it to them to place it on the trailer that they made for me. They neglected to put the rear-most floorboard over the lip on the transom tongue-in-groove. This is spotted by SIBRider in the pics i posted.

This cause the floorboards to fail to stretch out the floor material properly, resulting in a hooked hull, which frankc correctly diagnosed.

Unfortunately, nobody at my dealership, nor the dealership I purchased the boat from had this on their radar. Instead, everybody focused on the height of the motor. I eventually had the boat back at my dealership to have a metal plate installed in the transom that would raise the motor over 2 inches (putting the AV plate about 1 inch below bottom of boat). When the boat was in for that, it was also re-assembled properly.

After raising the motor 2 inches and properly assembling the floorboards, the hooking of the hull was pretty much solved. I could actually achieve WOT, while I hadn't been able to even come close to that before because accelerating beyond plunge speed pushed the bow down so hard. This workboat rides a little flatter than my previous Grand Raids, so that took a little getting used to. However, since the motor was raised, I started having a new problem: ventilation. The ventilation also prevented me from running the motor in the third trim pin hole away from the transom (because the ventilation became incessant with the motor trimmed that far up), which also caused a bit of a bow down attitude. I tried different props, including a 4-blade prop with no improvement. (In fact, the 4-blade was associated with *worse* ventilation.)

I finally had the transom plate removed and the motor brought back down to its original position. Now the boat runs perfectly. 24 mph today. Nice plane at WOT and no ventilation, even during turns, with the engine in trim position #3.

It's taken me several years to sort this all out, but I wouldn't have been able to explain it all at this point without all of the help I got here. I am just amazed that nobody at either Zodiac dealer (one of which is the largest dealer in NA, perhaps even the world) was able to bring incorrect floorboard assembly up in the troubleshooting of the obvious hull hook that I was describing. Hopefully this thread might be of help to someone else.

My problem underscores the importance of the correct floorboard length and assembly, so maybe this will be helpful to anybody considering manufacturing a floor for their SIB. I now strongly suspect that the OP's boat had an after market fibreglass floor that was too short...

Squid Boat · 25 May 2015, 04:03

Wow, what a journey, glad you got it sorted. Cheers to the guys that gave ya the clues. Thanks for documenting it for future owners mate.

All the best

Projectile · 25 May 2015, 13:24

Quote:

Originally Posted by frankc

I had to lengthen the front floorboard in a 10 ft Avon to cure a problem like yours. I was about to trash the boat until a nice lady from Achilles clued me in and recommended the cure. New lengthened floorboard and the boat is still in service after many years with no problems.

frankc, do you recall how much the floorboards had to be lengthened to solve the problem you were having with that AVON?

frankc · 25 May 2015, 15:30

I cut a mock up of the front panel long enough that it would not fit and then trimmed the length until it could be forced in position. This stretched the bottom fabric and prevented a hook in the fabric at the transom. The Avon then ran as well as it had when new or possibly better.

There are no anti hogging strips on this hull and the Hypolon stretched in use over time (hogback). If you see a cupped area in a hull ahead of the transom, it must be removed for proper operation of the boat. The area immediately forward of the transom has much to do with the performance of a hull.

prairie tuber · 27 May 2015, 05:04

Wow what a saga! When I lived in Manitoba, we had a Zodiac dealer who really knew his stuff, because he used a variety of the models quite extensively, including an expedition in Mark II Grand Raids from Winnipeg to Hudson's Bay at Cape York.

When they retired and sold the business (which also carried ATVs, dirt bikes outboards & snowmobiles), the new owners carried zodiac for a year or two, then discontinued carrying inflatable boats altogether because they were clueless about them. A few years later another marine place picked up the Zodiac line, but none of the guys there were at all familiar with them either.

A website like Rib.net really is a far more valuable (and far cheaper) resource than the vast majority of dealers out there.

jonp · 27 May 2015, 10:41

My cav (antiventilation plate) sits about 1in above the keel on my Zodiac 550 tour with a 70hp.

Depending on what you mainly use the boat for will depend how high or low you place the engine, check out this http://www.killcaremarina.com.au/ind...questions.html

Jon

Projectile · 27 May 2015, 12:02

Quote:

Originally Posted by prairie tuber

Wow what a saga! When I lived in Manitoba, we had a Zodiac dealer who really knew his stuff, because he used a variety of the models quite extensively, including an expedition in Mark II Grand Raids from Winnipeg to Hudson's Bay at Cape York.

We bought our first 2 Grand Raids from John Dubois in 1980 and 1981 and I remember him and his family very well. I used to love the drive to Lockport to check out Zodiac's latest offerings including a test drive on the Red River, once in a MkVIHD with a 235 Evinrude on the back - what a blast! He was a real enthusiast, and it rubbed off on us.

Good times.

prairie tuber · 27 May 2015, 13:49

Small world! John made a video wherein he drove his Chevy Suburban to the edge of the Red River with that Mark VI & 235hp Evinrude (with a tiller handle) in the back of the Suburban. He proceeded to pull boat and motor out of the back of the truck, inflate the boat with a 12v pump, assemble the floorboards, install the motor on the back, then drive the suburban up ramps and onto the Mark VI. They strapped the Suburban on to the boat then proceeded to drive the boat a few miles down the river to Lower Fort Garry and back!

Now that is extreme sibbing!