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  #11  
Old 03-05-2007
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re 'The perfect boat'

tartan34c (RobertGainer)..regards..tried to send you a 'quick response' so iwould'nt bother the other viewers..but the system did not accept..so posting the usual way. Thanks for the response..yes the only boats that have the above criteria (except affordability) are the lifeboats owned by the coastgaurd...i'm trying to design one that is affordable..
I checked proffessional boat builders site and scanned the articles but could not find it..can you be more specific..i would really appreciate it...
tho i did find the site extremely interesting, and hopefully will find some answers to questions..since it seems a site for marine architects/boat builders/boat designers and the like.
You too belong to this category (from your profile)..so would you be interested in kindly answering some of my technical questions?..your response was the only one that took my post seriosly.
I have already made a small toy model that fullfils all the criteria..and now in the process of figuring out how to proceed...as i mentioned i would like to develop the first prototype in the range of a 20 footer moterboat.
The problem i'm having to work out now is the self-righting part....in a sailing boat its easy with an appropriate keel and/or a ballast tank....however in a motor boat??...it could have a V-hull..with appropriate ballest..but the probably is not enough, unless you add a keel.
My first question is: how much would a keel hamper the boats speed?..are there formulas or charts that would guide me to limit the keel to a minimum?
Again remember were talking about a powerboat..actually one with an outboard (which is bad for its higher center of gravity)..
second question: if i choose an already manufactured boat that fits the initial shape and dimension..and plan to modify it to fullfill all the criteria of 'the perfect boat'..what would be the best way to attach/join the keel?..and where would be the optimum position?..i guess i'll have to build a test tank to test that..or what do you thik?
I've got a whole lot more questions..but i'm not sure if i'm boring you..so i'll quit for. By the way i have done a lot of reading regarding buoyancy, displacement, displacement-length ratios, cg, cb, righting angle..etc..and have no problem regarding handling the 'unsinkable', 'self-bailing' and the 'multiple means of propulsion'..and its the 'self-righting' design in a powerboat is the the problem.
Thanks.
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  #12  
Old 03-05-2007
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A powerboat designed to overcome hull speed needs to plane to reduce hull friction. The breadth and the relatively flat bottom of said hull requires the deck and superstructure to conform to it's design. That would make such a boat float as easily upside down as right side up. If you were to add a keel and ballast there would be too much surface area and weight to the boat to be able to get it up on plane with any reasonable amount of power and only make it more difficult to capsize. It could still be capsized and would not come back over, just sink faster with the added weight.

Don
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  #13  
Old 03-05-2007
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ZM, don't take these guys too seriously, your opening question was a little vague.
You have asked some good ones now, I'm sure you'll get some good answers.
The Coast Guard does have some boats that meet all the criteria you've laid out, but I don't know where you could find design plans. I've seen them at work(play) out of Morro Bay. Some of the things they do would scare the sh---poop out af anybody.
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Old 03-05-2007
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Quote:
Originally Posted by donrr1
A powerboat designed to overcome hull speed needs to plane to reduce hull friction. The breadth and the relatively flat bottom of said hull requires the deck and superstructure to conform to it's design. That would make such a boat float as easily upside down as right side up. If you were to add a keel and ballast there would be too much surface area and weight to the boat to be able to get it up on plane with any reasonable amount of power and only make it more difficult to capsize. It could still be capsized and would not come back over, just sink faster with the added weight.

Don
Do you think stepping the hull(like they do for race boats)would help break the keel loose of the water?
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  #15  
Old 03-05-2007
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sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
zmfmd-

I do believe my response was rather serious. As this is sailnet.com, not a general boating site, I responded with one possibility among production sailboats. However, it only meets three of your five criteria.

Multihulled sailboats, are also relatively unsinkable, can be affordable, have multiple sources of propulsion and could be self-bailing, but can not self-right.

Etap does market their monohull sailboats as "unsinkable". They are built with sufficient foam between the double hulls to keep them afloat.

Their keel provides them with a significant measure of self-righting capability.

They have multiple means of propulsion—sails or the inboard diesel—which is generally not the case on powerboats.

However, they are not self-bailing. They require bilge pumps, either manual or electric, to empty the boat of any water that has entered.

Nor are the affordable... Etaps, even used, are fairly expensive boats to purchase.

Most of the pilot boats or rescue boats are fairly expensive boats, and fairly narrowly marketed for a specific purpose. I don't see how a small outboard powered boat meets your critieria, unless you are planning on rowing it as an alternate form of propulsion.

Most boats are designed for specific purposes, and certain design requirements, like self-righting, put obvious constraints that are often unrealistic on the boat's design. Given, that people have been designing boats for thousands of years, don't you think that if it were possible to have one boat design that could be affordable, unsinkable, self-bailing, self-righting and powered by multiple, independent sources of propulsion, that someone would have done it by now?

Some of your criteria are contradictory. Having multiple, independent sources of propulsion generally increases the cost, making it less affordable. If something is unsinkable—is there really any need for it to be self-bailing???

Powerboats are often designed specifically for the purposes they will be used for. A keel makes a shallow draft difficult... it also makes it very unlikely plane successfully.
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  #16  
Old 03-05-2007
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I guess you could step the keel as well No wait.... think about it.......

Don
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  #17  
Old 03-05-2007
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Zmfmd,
Making a powerboat self righting is easy and you donít need a keel or ballast. Think about how stability works. There are two types of stability, first is form stability and second is stability from weight. A log will roll or just sit wherever you place it until you add a weighted keel. Then it has stability from ballast. Tip the log and it will return to upright because of the weight. Or take a flat bottom boat and you have stability from shape. As the boat rolls the center of buoyancy moves outboard of the center of gravity so gravity makes the boat returns to the upright condition without adding any ballast.

If you want a self-righting powerboat without ballast you need to add volume up high so that when the boat is on her side on upside-down the volume is ďon the other sideĒ of the center of gravity and the volume will roll the boat to a point where form stability will take over. In other words make the cabin very high and narrow so it provides volume far away from the center of gravity. And if you make that volume large enough to float the boat while upside-down with the hull out of the water the boat canít stay upside-down very long because she is more unstable there then right side up.

Tank testing is easy and we do it all the time. But we donít use a tank. We tow models early in the day on the Hudson River and get all the information we need. There are well known relationships between models and full size boats and if you are interested I can point you in the right direction.

I will look in my copy of Professional Boatbuilder when I get back to the office and will let you know which issue the article was in. SNAME has publications on this subject and RINA has some great stuff about British lifeboat designs. You will need to read up on this before you go too far. Most text books on Naval Architecture donít have much information thatís useful for something like this because not many boats are designed for this. The papers published by SANME and RINA are a better resource for this.
All the best,
Robert Gainer

SNAME and RINA are Society of Naval Architects and Marine Engineers in America and The Royal Institute of Naval Architects in Britain
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Old 03-06-2007
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thank you for piping up. you and I must have keyed on that sentence immediately...you said what I was thinking more eloquently than ever could I. Thanks, M6
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Troubling

Quote:
Originally Posted by camaraderie
"and i mean all boats whether sailboats, powerboats small or large will be built that way..similar to whats happening in other idustries..e.g. car air-bags are a must..etc.."

Yeah that's want we want...more regulations...less freedom and boats built the way YOU want them to be. It's for the good of the children I'm sure.
thank you for piping up. you and I must have keyed on that sentence immediately...you said what I was thinking more eloquently than ever could I. Thanks, M6
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Old 03-06-2007
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camaraderie
regarding the comments the it would impose more restictions and cause less freedom..that was not my intention at all, just imagin that you go to to buy a particular boat..and the agent tells you we have a similar model with the options that it is unsinkable. self-righting andself-bailing, that will cost you 20% more ..would you be interested?..no body is imposing anything on you, its your choice...
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