Aqua Marina - Budget Tunnel Hull SIB

[Old seahorse]

Very impressed at your efforts ( and determination!)
The trim tab may do the trick.
I have been trying out options to partially enclose my transom
(It’s made up of two parallel tubes with transom plate bolted in centre), just to avoid losing things out the back.
Still working on options.
Good luck with your trials

[Fenlander]

>>> confident it will be more a ‘work straight out the box’ scenario.

I completely forgot to draw attention to it but when I was on my private test track yesterday the Elling popped on the plane with the OB gripping the water like a good un and not a hint of ventilation. Most impressive... and thank goodness.

The 8hp will be the experiment as you say. You and I plus others have been vocal in our opinions in the past... based entirely on assumption and logic... so I'm looking forward to a fair real world test from someone with loads of portable OB experience.

[chipko]

Finally managed a few hours on the water this week and now getting little to no ventilation in chop. Different heights suiting different motors so the quick change riser pads useful and now getting a solid 14/15 knots from the 27kg Chinese Orca 8hp (feels more like 6hp tbh) 4-stroke running stock 7.5 x 8” prop.

To be honest, although great fun, reckon these little cat’s are probably more suited to small motors at displacement speeds. Once planing you’re in for an exciting twitchy ride in anything more than glass smooth water. With small dia. tubes and no drip moulding to the rubbing strake it’s a fairly wet ride in any wind and chop. Better performance to be had going into wind/chop when the air cushion works well to keep bows up. Going downwind slower to plane and rather susceptible to a fair bit of bow steering and semi submarining (losing air cushion and sucking bow down) in choppy conditions. Razor sharp reflexes required but great fun nonetheless.

All in all a good value no frills little boat and ideally suited as a super lightweight beach based fun runabout or tender. Wouldn’t recommend as your only/main boat for more serious use, and in no way as competent as say the much larger tubed cats like the Takacat/TrueKit/Elling.

Had great fun experimenting and getting this tiny super light cat to work, but realistically after a bit more seakeeping to cope with mixed conditions use.

[Old seahorse]

Hi Chipko, good to see you are having fun with your boat. It’s certainly a different experience! My takacat has generally been a really dry ride, but I launched off the beach into a bit of surf recently. I took a couple of waves head on, and took on plenty of water. Thankfully, it went straight out through the open transom, but it certainly cooled me down on a very warm day!
As you say, they have their limitations, but in the right conditions, they are great

[PapaWhiskey]

Hi, I just joined the forum after reading your experiences with the Aqua Marina 2.98 and hoping you can advise on the best engine choice.

I've just ordered one as a smaller light weight replacement for my existing 3.2m airdeck and Mariner 6 which at 48kg + 27kg is just getting too heavy for its main use as a tender to my offshore cruiser.

Having read your thread, I'm thinking the 2.98 with a Mariner 3.5 at 28kg + 17kg would be a well matched rig that seemed to work well for you at speeds up to 13knots using the long shaft version with no modifications to the transom height.

I'd very much appreciate your opinion and any further comment/advice on the above configuration.

Thanks, Peter.

[beerbelly]

that should work fine i bought one also and found the 3.5 worked fine but mines a short shaft and suffered bad propslip at the higher end of its speed range

[PapaWhiskey]

Thanks beer belly. Just need to be fairly sure there aren’t any issues going for a long shaft that would make it a bad choice.

[PapaWhiskey]

I’m hoping to order one this afternoon and save 10% on a promotion that ends at 5pm.

[PapaWhiskey]

Hopefully, chipko will drop in with his experience...

[PapaWhiskey]

I’m not looking for outright speed but will want to run it as fast as a 3.5 can go without obvious issues or needing transom modifications etc. I’ll be using it as a boat to shore taxi and exploring creeks, rivers and estuaries. I’ll be happy if it does 10-15 knots without any handling issues or skittishness

[PapaWhiskey]

If the long shaft proves too long, I could fit a raising pad like chipko if that would work better

[chipko]

Sorry just seen this. I’ll try and reply later but bottom line, don’t bother unless you just want a beach toy. All my findings are well documented earlier in this build thread.

[chipko]

Originally Posted by chipko

Finally managed a few hours on the water this week and now getting little to no ventilation in chop. Different heights suiting different motors so the quick change riser pads useful and now getting a solid 14/15 knots from the 27kg Chinese Orca 8hp (feels more like 6hp tbh) 4-stroke running stock 7.5 x 8” prop.

To be honest, although great fun, reckon these little cat’s are probably more suited to small motors at displacement speeds. Once planing you’re in for an exciting twitchy ride in anything more than glass smooth water. With small dia. tubes and no drip moulding to the rubbing strake it’s a fairly wet ride in any wind and chop. Better performance to be had going into wind/chop when the air cushion works well to keep bows up. Going downwind slower to plane and rather susceptible to a fair bit of bow steering and semi submarining (losing air cushion and sucking bow down) in choppy conditions. Razor sharp reflexes required but great fun nonetheless.

All in all a good value no frills little boat and ideally suited as a super lightweight beach based fun runabout or tender. Wouldn’t recommend as your only/main boat for more serious use, and in no way as competent as say the much larger tubed cats like the Takacat/TrueKit/Elling.

Had great fun experimenting and getting this tiny super light cat to work, but realistically after a bit more seakeeping to cope with mixed conditions use.

Can’t really add much more to my previous post above.

Had a blast last year messing about and modding the tiny Aqua Marina, although in the end not for us and sold on.

In summary, 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 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.

It’s a wet, twitchy, ride at planing speeds in anything other than glass smooth water requiring razor sharp reflexes…immense fun though.

[PapaWhiskey]

So did you find it wet and twitchy with the 3.5 long shaft as I don’t want a motor heavier than 20kg?

[chipko]

Originally Posted by PapaWhiskey

So did you find it wet and twitchy with the 3.5 long shaft as I don’t want a motor heavier than 20kg?

At planing speeds in choppy/breezy conditions yes. Slightly less with the 3.5’s as slower, maxing out at 11 knots (short) and 13 knots (long). Unfortunately at under 3m long, with small dia. tubes and a rubbing strake lacking any sort of drip moulding wind blown spray comes straight back in. It’s a twitchy ride and susceptible to bow steer, losing the air cushion and semi submarining particularly going downwind/following sea.

The longer 3.5 U-Deluxe or 3.35 Aircat may be considerably better in sea keeping and the Aircat’s appear to have shallower transoms…far more sensible.

Whilst the 3.5 longshaft was an effective quick fix regarding ventilation issues I’d not recommend running one as a permanent solution…it’s just so wrong.

As a super light ship to shore tender/creek explorer running at mainly displacement speeds then eminently suitable in my opinion.

[PapaWhiskey]

Thanks chipko for taking the time to post all the photos and reports of your testing and your constructive comments which I for one have certainly found extremely useful.

I was mainly attracted by the cat C rating, light weight and low price of the Aqua Marina whilst not loosing too much space or capacity against my existing 3.2 sib/6hp Mariner which has been absolutely brilliant and capable of 18 knots solo and 15 knots loaded with the wife and dog remaining totally stable and predictable in all conditions encountered.

I do realise this lightweight low bow 2.98 is not going to have the speed, sea-keeping or dry ride qualities of my existing rig but as I'm getting on a bit, 49kg + 27kg has become increasingly difficult to move around on and off the mother ship so i'm just going to have to compromise!

Best wishes to you and yours for the new year.

[Budgie boi]

Hey there. I have an aquamarina aircat 335 with a parsun 9.8 2 stroke. Was helpful finding this forum and these posts. The aircats transom height works well. Still some ventilation but a bit of moving around with two people on board gets is sorted. Once on plane down wind sitting back a bit helps and sitting forward into the wind reduces ventilation. 3/4 throttle is 15 knots with 170kg of humans on board plus some gear and it still planes with 3 adults at 230kg. Best value boat I could find new at $1100 NZD and motor was $2200 NZD.

[rgoers]

I know this is an old thread, but just wanted to acknowledge that it contains A LOT of very useful information... so thank you to all who contributed for all the technical knowledge. I have had my own adventures starting with a BRIS 9.8' SIB with a 4 HP Suzuki, then a BRIS 11' inflatable cat with a 15 HP Suzuki, and today my AM Aircat 335 should be arriving. This thread will prove invaluable in getting it all set up to fly!!!