Decking below waterline?

Or he could try one of my designs, but I suspect I've pissed him off.



I'll leave Blueheaven alone with mention of a magazine, I'm sure he wouldn't have. The last page is a the "Parting Shot" feature that I always enjoy and it's by fellow forum member Eric Sponburg. It's about this precise subject.

The magazine is called Professional BoatBuilder and it's produced by the WoodenBoat folks. It's not too interesting for the average person as it's a trade publication, but the April/May issue is the one I'm referring to. So, if you would Blueheaven, log onto > http://proboat.com/ < and sign up for the free digital issue of ProBoat. It a painless and free process. Then go to the very last page of this issue.

 

Sheesh. Well thanks all, for the *private* messages. My original question, regarding whether it was common practice to locate the cabin "sole" below the waterline has been answered.

I am about 5% into this design and learning as I go along. In my primary line of work, it is custom to submit to a preliminary design review at about 50%. When I get to that point, I shall upload my labours. I look forward to comments from anyone actually interested in *encouraging* new designers.

 

Well, I haven't offered a "private message" but have you preformed a weight study yet? Center of areas?

 

We would "encourage" you to be careful and also visit

http://forum.woodenboat.com/showthr...s-about-online-forums&highlight=eric sponberg

All other advice is offered without prejudice to ourselves and our connections.

 

Professional BoatBuilder

I'm an average person, but nevertheless found it interesting.

It's painless once you know that the digital reader assumes you have a US keyboard. (@ is Shift-2, and it's best to avoid symbols in your password).

Thanks for the tip!

 

EC

By your own admission you are an above average guy with your interest in boat building. What's your opinion of Eric's Parting Shot?

P

 

Many here who are essentially amateurs in boat designing have been just where you are now. Designing your own boat and then building it is way out there in the way of most satisfying things that a person can do. That holds from a simple flat bottom skiff to a complex cruising boat that can support you in grand style in all reasonable conditions. If you have the drive to do it and are willing to go through the learning curve before making a mess of things, then go for it and all good wishes to you.

If you allow PAR's advice (which is damn good, by the way) to upset or discourage you, there is practically no chance of success since there will be much greater obstacles down the road. This is probably the best forum for any serious discussion of boat design on the net. Witness the number, and worldwide spread, of professional and knowledgeable amateur contributors. There are however, sharks as well as life rafts in these waters and no clear means for the unwashed to know one from the other. Access to and skill in in the use of a computer is no guarantee of success either. One of our forum professionals, Eric Sponberg, has a pointedly applicable editorial on the last page of the latest "Professional Boatbuilder" magazine on this very subject.

The internet and its forums have created a connectivity between boat people that never existed before and most of us love its good side while, at the same time, are very wary of the pitfalls. Even at it's best, the internet is not a suitable substitute for individual study in the traditional forms of books, experience or more formal training. By all means, keep at the pursuit and best of fortune to you.

Since you have designed or built an ultralight, you must know that is far more exacting and critical than the average boat and should understand the critical advice being offered. The key word is critical, which may have been interpreted as negative. There is a great difference between the two concepts. I have also been helping build an experimental aircraft that is set for its first flight in June. That project has rested on the shoulders of great numbers of those who have, as offered by Perry, paved the way.

Proboat is my choice of the best boating magazine that comes to my mailbox, bar none. Eric's sentiments have been expressed often here by me and many others.

 

I think he's playing to the gallery by publishing that in a trade rag, but I agree with pretty much all of it.

Having said that, a keen amateur can go a long way with some of the software out there. As Eric said in another of his articles, you can now easily design a hull and calculate the hydrostatics using off-the shelf software.

The Naval Architect's job has changed from performing manual graphical integration of 2-D drawings to operating the software and interpreting the results. There's no reason why an amateur with some sort of engineering or technical background should not be able to do this himself for a small project, as we see in a lot of projects on this forum.

 

I have been in a boat that got swamped in very light conditions. Once it starts, there's positive feedback of sinking lower into the water as more water is coming over the sides. (In my case we were rescued and the boat recovered; it was in a race, rescue boats were close by)

You probably need to look at the ratio of the deck area below the waterline to the area of the waterline. So if your deck is 80 sqft and the waterline is 160 sqft, then the ratio is 50%, and your boat will sink by 1/2" for every 1" of water on the deck.

At some point you will reach equilibrium, where the water on deck is at the waterline. With drainage holes at this point, the boat will not sink any further if water comes of over the sides.

If your deck is 4" below the w/l, and the ratio is 50%, then you will need 8" of water on the deck to reach that point. If you can reduce the ratio, you'll reduce the amount of water on deck under swamped conditions (20% ratio, and you only have 5" on deck, etc.). You could raise part of the deck, with a step or slope, or put seats filled with foam, to reduce the area of deck under the w/l.

Your design should allow for continued running when swamped, by ensuring the cabin does not take on water, and you can still access engines, pumps, batteries, etc.

 

EuroCanal, I'm not sure of your experience, but do you know what PPI is? In short can you attempt to clarify the gibberish above? As for "continued running when swamped", well I think this stands for itself and would be a unique SOR addition to say the least.

 

I have sunk more than one.

Apparently PPI is the weight, in pounds, required to sink the boat by one inch. (It's time you guys switched to metric - it's much easier)

If the waterline area is 160sqft, the the PPI is 160x5.3 = 848lb.

Similarly, if the deck is 80sqft, then 1" of water on deck weighs 80x5.3 = 424lb, which will make the boat sink by 1/2" (80/160).

If the deck area is less, the boat will sink less. The gibberish above was an attempt to point out this relationship.

OK, agreed this sounds stupid when quoted back to me. I meant that the boat should continue running with a certain amount of water on deck.