Ribcaft 6.8 transom clearance cat 3 survey

[Boatserv]

Just was about to get my vessel surveyed however we had an issue with the transom clearance. Has anyone else had issues?

[diver 1]

I think its a common issue on many ribs inc earlier RC in achieving the nominal 250mm freeboard requirement in all laden conditions. Lots of solutions on here. Fugro have a 6.8 work rib which has a false second transom clamped between the tubes at the forward face of the A frame. On mine I've fabricated a small GRP well around the cut-out in the transom which effectively raises the height of the transom and works well without compromising any deck space. Delta ribs often come with an in house solution from new. Google images of Delta ribs and you'll see what I mean. Good luck

[diver 1]

Here's some examples of solutions I've seen

[mikehhogg]

can a vessel with an open transom attain cat 3 or 4. My halmatic has a transom height of 150mm. I don't do any commercial so wouldn't be familiar with the regs. some open transom boats are round the world yachts.

[GuyC]

Originally Posted by mikehhogg

can a vessel with an open transom attain cat 3 or 4. My halmatic has a transom height of 150mm. I don't do any commercial so wouldn't be familiar with the regs. some open transom boats are round the world yachts.

Mike

I'm surprised that your freeboard is only 150mm I think you might be confusing height of transom from the deck and freeboard.

If your waterline is co-incident with the top of the sterndrive, which is where mine is, it will give you 250mm freeboard.

I think possibly the P22's were designed to a rescue boat code that probably also included a 250mm transom freeboard requirement. This is a bit of conjecture though.

The regs only seem to give you some slack in transom height if you operate in Cat 6 waters.

It doesn't help the OP though.

[mikehhogg]

mine is jet drive and is lower than stern drive transom and your right my measurement is deck to transom. Has the pac in pic been modified to meet regs, sorry for hijacking original post

[GuyC]

Originally Posted by mikehhogg

Has the pac in pic been modified to meet regs, sorry for hijacking original post

No, I don't believe it has.

[GuyC]

Originally Posted by diver 1

I think its a common issue on many ribs

I wonder if it is as a result as a result of trying to get the outboard low enough to get the cavitation plate at the right height. It would be particularly difficult on boats where the deep vee wasn't truncated by a planing pad. I think RC's have a 'full' dep vee.

It sounds like an inner transom would be a sensible way to go. It would have to be sufficiently structural to withstand a head of water equal to its height as if the boat is swamped, it would be the inner transom that would be resisting the pressure before the elephants trunk or freeing ports could get rid of the water.

Whilst the well that Diver1 has fabricated seems to work I can imagine a surveyor might look at the volume of water the well could hold before it gets to deck level and say it is not big enough. I've done a similar thing when customers don't want a coaming in way of a weathertight door and we've created a well in front of the door. They are a reasonable distance above the waterline though.

[Boatserv]

Thanks Diver1, that is the way i am going. Will update the thread once complete.

[Rib_Tickler]

Hi Boatserv

Where did you get to with this mod you all coded now?

Thx Dave