Aqua Marina Aircat 335 Ventillation Issues

[smallribber]

Originally Posted by knwatkins

I've got it in the bottom hole so the leg is closest to the transom as it can be. I did attempt to experiment with it when I was out on the water but unfortunately the pin fouls on the wheel brackets so I'd have to remove the motor to trim it to a different position.

Am I right in thinking that when trimmed down/in, this is best position for reducing ventilation?

Yes Trimmed in/down is best for stopping ventilation

[smallribber]

Originally Posted by Nasher

I would agree that the combination of the fins and the engine being trimmed right in might be lifting the stern and forcing the Bow down too much.

I think you need to test the 9.8 trimmed out a couple of holes and without the fins as a more normal starting point.

.

I think you might be correct about moving it to hole 2 or 3 from the transom

[knwatkins]

Thanks all. Unfortunately I cannot remove the thrust road with the engine in situ on hole 1 when out and about but I've just thought - I can use the rod from my 5hp Tohatsu so I will take that out with me and trim it up/out to see what effect it has.

I've now removed the hydrofoil too. I will hopefully be able to get out on Friday afternoon for a test run and will report back with the results.

[Steve509926]

Hi, before you go at the transom with a saw are you sure a small cat is the right sib for you with two toddlers.
I've often thought I'd like to have a small cat, then I read the reviews again and the one thing they all have in common is what a wet ride they are. I think the first few times your girls get wet they'll think it's great, but the fun soon wears off when they start getting cold as well.
Just a thought.

[smallribber]

Originally Posted by Steve509926

Hi, before you go at the transom with a saw are you sure a small cat is the right sib for you with two toddlers.
I've often thought I'd like to have a small cat, then I read the reviews again and the one thing they all have in common is what a wet ride they are. I think the first few times your girls get wet they'll think it's great, but the fun soon wears off when they start getting cold as well.
Just a thought.

I have not said this but I think Steve is correct. That CAT is a lovely fun boat but it is just that a sort of hoon about on a nice day for 1 or maybe 2 people. I think a proper sib would be better for you and your little ones. I will of course suggest a Honwave T38 IE3

[craigh]

Some good advice on here, but as you mention you are new to sibbing, worth mentioning the absolute basics.


As they are so light, subs tend to be very affected by correct weight distribution. I spent several frustrating days before I found I needed to reposition myself a lot further forward (as far as I can comfortably sit and reach the tiller), and also move as much weight fwd as I could.



They also need the floor to be at correct pressure (and remember on a hot day when you inflate on land and put into colder water, pressure will drop a bit)

[knwatkins]

Thanks chaps and yes it's a very good point. In all honesty, I don't think we'll be taking it out in the winter at all, we're probably going to be fair weather sibbers only. I might get out on it on my own now and then in the colder weather when I fancy blowing the cobwebs away. It was pretty choppy in the harbour last weekend and there was a bit of spray when we were head on into the wind, but it was alright actually. At the moment, I'm willling to see how it goes.

Maybe in the future we will upgrade but as this is our first one, we are limited on budget. I managed to pick up the Aircat for £450 including the launching wheels. When I was looking around, I came to the realisation that I would be paying a lot more for a proper SIB with a closed bow.

[knwatkins]

Originally Posted by craigh

Some good advice on here, but as you mention you are new to sibbing, worth mentioning the absolute basics.

As they are so light, subs tend to be very affected by correct weight distribution. I spent several frustrating days before I found I needed to reposition myself a lot further forward (as far as I can comfortably sit and reach the tiller), and also move as much weight fwd as I could.

They also need the floor to be at correct pressure (and remember on a hot day when you inflate on land and put into colder water, pressure will drop a bit)

Thanks Craig. Our engine came with a tiller extension so I have tried sitting further forward and using the extension but it still ventilated unfortunately.

On the pressure side of things - that's a really good point, I wouldn't have thought of that. I'll have to get myself a little plug in pressure gauge to monitor the pressure.

[chipko]

Bit late to the party and plenty of good advice from others so far.

Just to clarify our little Aqua Marina was the smaller 2.98m U-Deluxe with the closed bow but still a tunnel hull. The transom was also a good 40mm higher than the Aircat 335.

In summary my findings were, couldn’t eliminate ventilation with our Mariner 3.5 short shaft despite cutting down transom by 60mm. Long shaft 3.5 worked ok on uncut transom with no ventilation although not an elegant or efficient solution…already had a long shaft aux on the rib and certainly wouldn’t buy one for this boat.
Best suited motor at the time turned out to be an Orca 8 (aka Yamaha 6hp clone) which suffered little to no ventilation with transom lowered around 20 to 30mm, seeing a scary 15 knots solo in ideal conditions.

Sold on as at the end of the day sea keeping wasn’t up to it for us and the small diameter toobs and flat rubbing strake gave a wet twitchy ride at planing speeds in anything other than glass smooth water requiring razor sharp reflexes…immense fun though. Yours being that little bit longer and the wide ‘landing craft’ open bow should scoop in more air at planing speeds and improve the ride.

Looking at your pics I’d be inclined not to cut the transom just yet, as the AV plate looks to be nearly level with underside of tubes which on most cats is the ideal. Worth trying without the doel fins and trimmed out a hole or two. Most cats ride much better with bows trimmed slightly high to get the air cushion working effectively. If still no joy then a cupped prop would be my next move and these seem to often cure the problem on even the most stubborn cats. Might need to go down on pitch as the cupping saps a bit of engine power….your tach will confirm this. Also try going out solo to see if problems subside….cats seem more sensitive to load/performance than conventional hulls.

If all this fails then by all means cut down the transom. Start with say 25mm and see what happens. You can always go deeper.

Good luck in your quest.

[Fenlander]

>>>I’d be inclined not to cut the transom just yet, as the AV plate looks to be nearly level with underside of tubes which on most cats is the ideal. Worth trying without the doel fins and trimmed out a hole or two. Most cats ride much better with bows trimmed slightly high to get the air cushion working effectively. If still no joy then a cupped prop would be my next move and these seem to often cure the problem on even the most stubborn cats. Might need to go down on pitch as the cupping saps a bit of engine power….your tach will confirm this. Also try going out solo to see if problems subside….cats seem more sensitive to load/performance than conventional hulls.


Chipko sums it all up above really. It may be this isn't the ideal boat but many of us don't get the right SIB first time and it was a bargain so stick with it for now and have some fun getting the best out of it.

I would comment getting weight forward with a SIB is something you often have to do to get on the plane well, particularly if slightly underpowered, but is not usually the answer for ventilation. Doing so can make cat types very twitchy with "bow steer".

[knwatkins]

Brilliant, thanks so much Chipko. Your U-Delux thread has been very informative to me and you've provided some wise words of advice. Subject to weather conditions, I'll be taking the cat out on my own on Friday morning to see how it runs with the 9.8 with no hydrofoil and trust rod on position 2 and 3.

Thanks also Fenlander. I will report back on Friday or over the weekend on the results of my experimentation.

I've started to put some feelers out there concerning a replacement prop with lower pitch and what it will cost me to get it cupped so if I go down that road as a next step, I'm fully informed.

[knwatkins]

Winds in the harbour are in the upper 20s today with gusts in the upper 30s so won't be going out today unfortunately :-(

[smallribber]

Now the weather has turned a bit. I might go out in my little Kat sometime in the old dry suit for a bit of fun

[Peter_C]

Of note I used to have a SIB and with a lower air pressure it would do a funny arch it's back thing, then release and the prop would slip. An air pressure gauge is a requirement for SIB's and RIB'S.

Good luck, hopefully you get it sorted quickly

[chipko]

Originally Posted by Steve509926

I've often thought I'd like to have a small cat, then I read the reviews again and the one thing they all have in common is what a wet ride they are.

Not sure what reviews you’ve been reading but in my experience quite the opposite. Odd that most think sib cats give a wet ride and the sea just pours in over bows. Owned, borrowed and tested more than a few including Takacat, Elling, Boatworld KatSport and Cruiser, TrueKit, Kolibri (even a Zapcat!) and not one has proved a wet ride. In fact probably drier than many monohull sibs. Water just does not come over the bow unless deliberately punching through breaking surf.

The only wet ride was with our tiny 2.98m Aqua Marina U-Deluxe, and this was more due to the small tubes and poor design rubbing strake with no water check than the tunnel hull design. Little more than a beach toy if honest.

[Steve509926]

Originally Posted by chipko

Not sure what reviews you’ve been reading but in my experience quite the opposite. Odd that most think sib cats give a wet ride and the sea just pours in over bows. Owned, borrowed and tested more than a few including Takacat, Elling, Boatworld KatSport and Cruiser, TrueKit, Kolibri (even a Zapcat!) and not one has proved a wet ride. In fact probably drier than many monohull sibs. Water just does not come over the bow unless deliberately punching through breaking surf.

The only wet ride was with our tiny 2.98m Aqua Marina U-Deluxe, and this was more due to the small tubes and poor design rubbing strake with no water check than the tunnel hull design. Little more than a beach toy if honest.

Hold my hands up! Just re-read your thread and a couple of others. In every one "wet ride" is mentioned, however not by the reviewers, perhaps that's what has influenced me.

[smallribber]

Originally Posted by Steve509926

Hold my hands up! Just re-read your thread and a couple of others. In every one "wet ride" is mentioned, however not by the reviewers, perhaps that's what has influenced me.

Always important to listen to those that have actually got and or tried the 'thing' in the real world.

[knwatkins]

So I managed to get back out on the water (Poole Harbour) this morning to conduct some testing.

Hydrofoil removed and motor trimmed out on holes 2 and 3 (started on 3, then moved down to 2). The result - much less ventilation

With the wind behind us, it was brilliant. She shot along with minimal ventillation.

However, riding into the wind was scary! The bow was so high in the air, I was worried we would flip over! This is probably a combination of removing the hydrofoil, trimming the motor further out and it was bloody windy!

My current prop is a 8.9x8.3. I've just ordered a 8.9x7 and I've spoken to a local prop specialist who will add some additional cupping to it.

I'll then try it again with the hydrofoil fitted to keep the nose down and the cupped prop to minimise the ventilation.