The Ultimate Sailing-Cruiser?

[Brasstom]

(Also posted in the Design forum)

Hello all! I've been browsing this site for about a year now and have finally decided to contribute something to these discussions! I'm also hoping for some constructive commends about an idea I've had for a few years now, since I first became interested in building sailboats.

First of all I have to admit to being a complete amateur in the field of boat design. I admit it because I'm sure it will become obvious soon enough! I'm an amateur builder with two small boats under my belt and am working on a 22 foot plywood sharpie design right now. But my dream boat is the one I'm going to describe now...

What I want is a sailboat with the capabilities of a do-it-all adventure boat. I'd like to build a boat with a length of about 50 ft and a beam of about 15 ft. What would make her unique is that in the center of the hull would be a 10ft by 8 foot bay, like a cargo hold, in which you could put either a very small 1 atmosphere or a decent sized ambient air dive submarine. The bottom of the sub would have clamshell-style doors which would open to lower the sub into the water when the sails are down and an anchor is lowered, providing stability. It would be lowered using a modifed boat lift-crane mecahism until it was below the bottom hull, where it could then shoot forward.

I'll try to get some of the rough sketches I have of this concept online as soon as I can, or email me. They're VERY rough, mostly drawn by an unskilled hand on loose scrap paper. Basically the deckhouse would look like a backwards C with the bay in the open part of the "C." Staterooms fore, galley aft.
This idea has been in my head for a long time and I know VERY little about boat design But I want to take this to the next level to make my dream some kind of reality and so I thought I'd start to trouble shoot the theory. There's MUCH more I have in mind for the design but I'm trying to keep this post to a reasonable novel-like length, lol. But in a nutshell:

I want to hang a very small ultralight seaplane off the back of the boat. The plane's exist and are very light, the greater issue is a stable storage rig for it. Maybe some kind of storage hold in the very front of the boat for a motor-bike or two, should I decide to go larger with the design.

Problems I see: <--and I KNOW there's more!
-Clamshell doors...how in the hell??
-Weight allocation and distribution, something I know very little about
-Mast or location or locationS
-the bay, which I think must necessarily go in the center, will make fitting two staterooms and a galley difficult...but not impossible, I think.

Well...please read, comment, and gimme a hand! Feel free to email me with questions, suggestions, ideas, critiscism (of the friendly kind I beg you!) or offers of help! Lord knows I need it!!

Thanks,
Tom

[Seafarer24]

This doesn't sound entirely unreasonable. The biggest problem I see is that when the doors are opened, you will loose a lot of buoyancy and the boat will settle deeper in the water. How much deeper depends on the weight of the boat and its underwater profile.

Aluminum would be your best building material. I'd say steel should come in second but I'm concerned about the weight of steel in this application, and the fact that you'll be flooding moving parts with saltwater regularly.

The second problem I see is the location of the bay. It needs to be put where it won't interfere with the keel (obviously the normal full keel is out of the question!). The keels placement will depend largely on what rig you plan to use. This seems to me like a prime candidate for twin keels (with bay door between them) with a schooner rig to keep the CoE over the CLR.

Are you on the PSubs e-mailing list?

[mackid068]

I believe that steel actually comes out to be lighter overall somehow. I had just heard this somewhere.

[Tim B]

The argument being that steel is stiffer and has a higher UTS that aluminium, so you can use less of it. It is still a lot denser, though, and corrodes like hell in salt water. Stick with Aluminium.

Sounds like it'll be a fun boat, also reminds me of something from a bond film...

Cheers,

Tim B.

[mackid068]

Aluminum, then. Sounds good. Go for it!

[marshmat]

Clamshell doors for sub: This is a Big Trend in 200-foot megayachts, having a docking submarine with a clamshell-door bay.
Hydrostatics, weights, etc: Given enough study, patience, guesswork and math, this can be sorted out. I certainly don't know how yet either, but you can of course learn.
Mast and keel will be hard to place, yep. An idea I've played around with now and then is a drive-in tender bay at the stern; this might get your sub clear of the rig but still, bays of any sort tend to be a motoryacht thing and keels/masts would get in the way. Twin keels sounds like a good idea here, as does schooner rig. So you're probably going to do a few hundred laps of the design cycle before you get there, but it'll be pretty neat in the end.

[mackid068]

I would drop the sub out of the rear, but place it on deck and have a center cockpit.

[Seafarer24]

A 1atm submarine is going to be very, very heavy. Nothing I'd want up on the deck of a 50' boat.

Aluminum is far stiffer than steel, however steel is ultimately stronger. You have to have more internal bracing, or thicker plating, to get a steel hull to hold it's shape (no oilcanning) as well as an aluminum hull.

When you want strength you go with steel, when you want stiffness you go with aluminum, or wood. Boat hulls generally need to be stiff rather than strong, as we try to keep them from hitting solid objects

[mackid068]

Very heavy? How heavy? Maybe in lieu of a 1atm submersible, you could try a sub where you're sealed from water, yes, but is a single person sub where you must use SCUBA tanks for air.

[marshmat]

Subs are heavy, yes. If you want a 1atm sub look at US-Submarines' Triton series http://ussubs.com/submarines/triton_650.php3 it only weighs about two tonnes in air. Of course a wet or ambient pressure sub will be much lighter on deck.

[mackid068]

A wet sub may be the best option in terms of weight, for your puposes. Also, make sure you have adequate facilities for retrieving the sub. Have a RIB on hand.

[Brasstom]

Thanks all for the comments! Some replies:

I've all but decided to abandon the idea of a 1atm sub in favor a semi-dry ambient air submarine. This will make my max depth 120 feet and will limit the amount of time a person can stay deep underwater but there are numerous reasons to prefer this style. First is weight, an semi-dry submarine, fully loaded, MIGHT weigh 3 or 400 pounds (if its big and LOADED). Thats nothing compared to a 1atm. The second is cost and ease of construction. The submarine (I'll attach a picture or two below) I have in mind will be constructed of plywood encased in fiberglass cloth and epoxy. Easy to build, easier to afford. The final reason is practicality. I'm not building a deep-sea explorer vessel, here. I'm designing an adventure yacht that "has it all" and is affordable.

A note on wooden hulls:
I'm opting for a wooden hull for two main reasons. 1) once again, Ease of construction. I can BUILD a wooden ship. I cannot build a steel, aluminum, or fiberglass boat. I'm sure others can, but my entire experience is with wood and this project is big enough with adding a whole new repertoire of skills to my inventory! 2) I LIKE wood. Its easily modified or repaired, its beautiful, its relatively cheap, and its fun to work with. If its at all possible, I'm going to get this thing to be made of wood.

The PROBLEM I am still hung with is my underwater door. I'm thinking of building the bay slightly off center (two feet towards the port side) which may help me bring it down to just having one singe door. Anyone have any ideas for how to build a door that, when closed, will be watertight? I don't care what the door is made of, I think aluminum may be the way to go.

I hope this answers some of the questions or concerns about this design. I've attached a picture or two of the submarine I intend to modify. I more than welcome all new and additional comments! Thanks, all!

-Tom

[Brasstom]

naturally I forgot the attachments. You can find them in the bottom of this thread:

The Ultimate Sailboat


or at this website:

http://www.scubatow.com/Sub.html

Thanks!

-Tom

[Seafarer24]

Well, since this will be light enough to place other than in the center of the boat, I'd now recomend a fin keel and skeg-hung rudder, with the bay doors between the two in an "aft cabin".

I also recomend making the doors out of the same material as the hull. Build the hull, then cut the plywood out where the doors will be. That plywood will already be shaped to fit. Laminate another piece of plywood to the inside of that for extra strength and reinforce the hull framing around this area. It's going to take large rubber gaskets around all the parts of the doors and some sort of very secure locking method to get it water-tight though.

With a 400# sub, the main boom should be able to hoist it out of a "Cargo Hold" style chamber and swing it over the side. While I know you're hung up on the bomb-bay door method, I think you'll find that it adds way too much complication in the construction of the boat to warrant it's use for a light-weight sub.

[mackid068]

Sounds good. A cargo hold type chamber, however, will, invariably, leak at some point and must be maintained AND not leak much to avoid sinking the boat from the inside.