420 air deck v floor pressure wave

Drewgrundy14 · 30 May 2018, 21:42

Hi all new here so be gentle. Tried out my newly purchased 25hp mercury mariner on my 420 prowave. Engine is great, plenty of power and very responsive. What I don’t like is the prowave floor develops a huge pressure wave when we start pushing it along. To me this really restricts the performance of the boat and must put a lot of stress on the whole thing.
I’m thinking of making a GRP clamshell sort of thing. Moulded to the same shape as the hull but make it removable. So that it can be strapped onto the underside of boat.
Anybody ever seen something like this before?

Fenlander · 30 May 2018, 22:17

Hello and welcome to the forum.

Your problem is common with 4m+ air floor designs as they lack the longitudinal stiffness to resist this pressure wave effect.

I think your clamshell idea would be far more effort and cost than just swapping onto a boat that better suits your needs.

willk · 30 May 2018, 22:24

Have you checked compartment pressures while afloat?

Drewgrundy14 · 30 May 2018, 22:26

Cheers Fenlander. It’s just s bit of an idea.
The 4.2m SIB suits us perfectly as I keep it at the caravan. Blow it up throw it on top of pickup and me n the kids are off. Easier than trailering a boat as I’ve nowhere to store it at the caravan. Just annoying to lose so much potential to the floor buckling.

Drewgrundy14 · 30 May 2018, 22:27

Willk. I haven’t to be honest
Checked pressures before casting off but not loaded in the water. Will do next week. Cheers

Fenlander · 31 May 2018, 07:55

Willk is right of course... I was jumping a step that might help... but pushing an air floor SIB your length at the speeds a 25hp would achieve is so likely to produce the occasional feeling of driving over a whale’s back I went straight to that thought.

But I was rushed last night... and full of Chinese seconds... so didn't give a complete answer.

SIBs can be prone to a feeling that I describe above as if climbing up the back of a whale and slipping down the other side sometimes with associated prop slip due to ventilation.

Air floors are worse than alloy/wood floors and the longer they are the more prone.

Factors affecting how any particular SIB is affected include tube and in particular air floor pressure... loading... distribution of load... sea state... amount of OB power... even down to prop choice.

Did you use your Prowave previously with another OB... if so what size and how was that? Can you describe exactly what you are experiencing to call a pressure wave and at what sort of speeds and in what sea state?

John Kennett · 31 May 2018, 12:33

As others have already said, check that the floor is at full pressure when you’re on the water. Apart from that you’ll just have a accept is as part of the compromise of having an air floor. It won’t damage anything though.

All flat deck air floors do this to some extent, and it particularly shows up in a chop or at speed. The bigger the boat the more pronounced it is, and I wouldn’t go much above 3.4m with this type of floor. Even then it’s going to be a bit floppy.

You’ll either need to live with it (and it may not turn out to be all that bad once you get used to it) or change boats. Options include:
- V floor inflatable (Aerotec or Honwave)
- Solid floor inflatable
- Small RIB (fully folding, folding transom, or conventional)
They all have their own compromises though.

Big Al C · 31 May 2018, 12:55

Quote:

Originally Posted by John Kennett

As others have already said, check that the floor is at full pressure when you’re on the water. Apart from that you’ll just have a accept is as part of the compromise of having an air floor. It won’t damage anything though.

All flat deck air floors do this to some extent, and it particularly shows up in a chop or at speed. The bigger the boat the more pronounced it is, and I wouldn’t go much above 3.4m with this type of floor. Even then it’s going to be a bit floppy.

You’ll either need to live with it (and it may not turn out to be all that bad once you get used to it) or change boats. Options include:
- V floor inflatable (Aerotec or Honwave)
- Solid floor inflatable
- Small RIB (fully folding, folding transom, or conventional)
They all have their own compromises though.

A few years ago.... got chatting to a bloke who had just bought new the 3.8 version of what you have. Was having the same problems..... unfortunately it would not go away..... even leaving it in the water for 20mins and repumping the floor with the high pressure electric pump.
As pointed out once you go past 3.3 /3.4 its not the best performing floor. Just to big an area to keep it's shape when being pushed against the water.
The bloke spoke to the supplier, was going to take it back after his weeks holiday and swop/partx for an alloy floor sib.

Drewgrundy14 · 31 May 2018, 13:11

Thank you all for responses. Yes used the boat with a previous OB an old 20hp Johnson which did similar but nowhere near as pronounced as experienced at the weekend. Was on the Menai straits so swell was minimum but lots of current. Would say the hump back whale starts not much after the boats starts to plane. Had 3 up 2 adults and 1 child plus fuel and some fishing kit. Looks like I’ll have to live with it till something else comes up.

Lee1 · 31 May 2018, 17:00

I get the same in a 2.7 v floor, I tried carpet fitted tight inside (when wet it weighed 40kg) and various options on top of that which helped slightly, I'm considering a wood floor inside the only problem is that it will put all the weight on the seams between the floor and tubes. Even if I sit on the floor the force of the water still pushes the floor up so I doubt their is a solution, it's the main reason I'm thinking of going back to a flat air deck boat with air keel
What's needed is a new boat design with air keel, removable flat air deck and rear air planning tabs!

Fenlander · 31 May 2018, 20:38

>>> it's the main reason I'm thinking of going back to a flat air deck boat with air keel

Of course your choice but they have the worse potential of all SIB designs for this behaviour.

The whole problem is caused by the flexible nature of a sib hull and is something the University of Southampton researched in tank testing for the RNLI regarding using inflatables in the rescue fleet.

As I have said before in such threads the following information is so no newcomer to SIBs who may be deciding what to buy is left confused...

The high pressure V air floor of the Aerotec prevents this totally... meaning if you need an air floor for portability but are sensitive to the issue then no new design is needed as it already exists.

A properly set up and inflated wood or alloy floor SIB with low pressure sausage keel will usually only suffer occasionally as the pressured keel has the hard floor to bear against so it keeps the outer floor skin tight most of the time.

The Honwaves and similar designs with the semi V high pressure air floor similar to the OPs Prowave suffer to varying degrees but really 3.8m is the absolute limit before they are very prone.

Slightly better than the final category below are the Zodiac Acti-V models which are a flat high pressure floor but with a taller high pressure keel linked to and inflated with the floor.

The very most prone are those with a flat high pressure air floor and a low pressure sausage keel underneath. Despite their floor being firm to stand on it doesn't totally resist the upward forces of the keel so will bow up in the middle which allows the outer skin to go momentarily slack when the water underneath acts against it causing the issue.

Lee1 · 31 May 2018, 21:23

It's agreed that an aerotec has the best keel in the SIB range but many people buy new or used sibs with a budget under £750, I personally brought a honwave t27ie when they first came out, I used it 3 times and sold it and went back to old avon's as I didn't like the boats internal aspects of the V floor. I think V floors have a good standing in the SIB world but are over rated, over the years since I sold my t27ie V I have acquired many many more of them in my dealings as a trader (all sizes from 2.7-3.8) they come up a lot as people that have them often move on to RIBs or aerotec etc. . . Every time a mint one comes in I say to my self I will keep this one for my personal use but once afloat in it I realise why I never do keep one, I even convince myself I should keep one just to be in the V floor gang lol. Ive also used the Sunsport V floor 2.7 and 3.2 it's no different from the honwave V floors. Europa have launched a V floor model as well now but it will be no different than the others, an inflatable v floor is never going to be the same as a ridged displacement hull.
In my years and years of using honwave V floors the best I found was a t2.7ie with a two stroke 10hp (it was over powered the rating for the 2.7ie is 8hp) and no kit i.e. as light as possible and it worked well. As soon as more weight was added as in a second or even third person it was pointless having a V floor. I've kept the Waveline 2.7 V floor as it has the capability of taking a 20hp weight when I have 3 people and kit and want more than 8 knots.
Personally I would have a flat floor, either wood, aliminium or air deck on top of an air keel rather than the V floor design any day for use as a family boat.
If you use a V floor boat you must sit on the seat thus distributing your weight over the tubes allowing the V floor to work, sitting inside the boat on the floor or tubes doesn't work.

John Kennett · 31 May 2018, 22:33

Quote:

Originally Posted by Lee1

If you use a V floor boat you must sit on the seat thus distributing your weight over the tubes allowing the V floor to work, sitting inside the boat on the floor or tubes doesn't work.

Sitting on the tubes of an Aerotec has always worked perfectly well for me.

John Kennett · 31 May 2018, 22:38

One alternative that hasn’t been mentioned is the Zodiac Futura FR which has an inflatable floor with “speed rails” instead of a keel. These are much less common than the other designs and I’ve never tried one.

Does anyone here have first hand experience?

Fenlander · 01 June 2018, 10:19

>>> Zodiac Futura FR which has an inflatable floor with “speed rails” instead of a keel. These are much less common than the other designs and I’ve never tried one.

No nor me... I've been close to buying a couple but they happened to be old bargains and I didn't want to go through the glue thing. And not having used one I didn't want to just make up something!

When you look at the hull it seems to have a V keel just a bit more pronounced than a normal SIB with the speed tubes to rise up on when on the plane. Photos of it in running show in other than flat water there would something of a trimaran effect.

From what I've read from owners they are superbly capable and stable but quite hard on the body at speed in rougher conditions.... perhaps because they often have bigger OBs and folks drive them harder than average SIBs?

You really need to want one at close on £4000 for a 3.7m air floor.

Fenlander · 01 June 2018, 10:24

I always liked the videos of a Futura from this guy who may be... or have been... a forum member??

https://www.youtube.com/watch?v=eQ_PgaTnqdU

Lee1 · 01 June 2018, 15:22

Quote:

Originally Posted by John Kennett

Sitting on the tubes of an Aerotec has always worked perfectly well for me.

I was referring to the honwave, sunsport and my Waveline V floor models

Fenlander · 01 June 2018, 15:57

>>>If you use a V floor boat you must sit on the seat thus distributing your weight over the tubes allowing the V floor to work, sitting inside the boat on the floor or tubes doesn't work.

Complete rubbish and absolutely misleading to anyone reading this thread and wondering about buying a high pressure V-floor Honwave style SIB.

Buy one and sit where you like.... like these guys doing a 60km round trip in a Honwave 3.8 with air V-floor and no seats fitted. These are folks actually doing proper distances on the sea and the floor looks to "work" for them.

https://www.youtube.com/watch?v=LO3A9xI0jQ4

Poly · 01 June 2018, 17:02

Quote:

Originally Posted by Fenlander

>>>If you use a V floor boat you must sit on the seat thus distributing your weight over the tubes allowing the V floor to work, sitting inside the boat on the floor or tubes doesn't work.

Complete rubbish and absolutely misleading to anyone reading this thread and wondering about buying a high pressure V-floor Honwave style SIB.

Buy one and sit where you like.... like these guys doing a 60km round trip in a Honwave 3.8 with air V-floor and no seats fitted. These are folks actually doing proper distances on the sea and the floor looks to "work" for them.

https://www.youtube.com/watch?v=LO3A9xI0jQ4

And strangely (:-)) I don’t recall anyone on either of the Scottish SIB outings I organised with either honwave or aerotech air floors having this issue... and they were travelling solo and combined must have done c 500 miles on those weekends in a mix of glassy calm to 2m high waves, sheltered coves to the corrywreckan...

jeffstevens763@g · 02 June 2018, 09:31

Couldn't you keep the keel and replace the floor with plywood or make a wood keel same as the bombard C4 with a wood floor more of a faff to put together but might satisfie you more in terms of performance