Sailing Dinghy Design

Tim B - Yup, weight can be a problem. Open transoms, however, are the norm for just that reason, plus the fact that they drain well. A "flase deck" as you say, just above the waterline, ensures that any water entering the boat quickly leaves. The ultimate self-bailer. If you want to stay dry, you won't be sailing one of these things ;-))
Keeping the inner skin curved does a great deal to stiffen it.
Steve

 

PS - That should be "flase" deck, not "flase". Danged spell-chequer isn't working rite again......

 

OK - I give up..... FALSE.
Phew!

 

I agree with Steve where ocean racers are concerned, but as drawn I don't think the false deck, a.k.a. cockpit sole, is high enough to keep the back end of the boat from sinking if someone moves aft while the boat is at low speed or stationary. Another thing pointed out to me by the measurer of the Classic Moth class is that without a cockpit sole it's possible to keep the boat stable while in irons by getting your weight low - an ability without which it's difficult to rest! The Moths all have bailers.

Two of the four Modern Moths were narrow, and one was indeed fugly. The Classic Moths are wide on deck because racks, trapezes, and hollows in section are not allowed....hence the V shaped midsection.

 

You do realise that when I mentioned sailing backwards I was talking about getting away from the pontoon!! I don't sail the whole course backwards... right, enough banter, down to business. I am still going to be concerned about the weight of a false floor until somebody gets the weights and proves me wrong. My attitude to this, and call me boring if you like, is to use a full-height transom, and bailers in the floor. This set-up works very well indeed (unless you sail my LARK). anyway, the structural gain is the strength of the transom which makes the boat altogether more rigid. If there's one thing I can't stand It's boats that flex. There is, therefore, now no need for the false floor, and a central stiffener can go amid-ships as normal (if necessary), and using a centerboard case, it assists in holding everything in place. this obviously represents quite a considerable weight saving. Of course, if we are below weight, it can always be made up by putting more down low. The other issue that I hadn't thought of this morning was the extra height (well, not from an ergonomic perspective), and so the final argument would be between the increased possibility of a confrontation between the boom and my (or the helm/crew's) head.

Stephen, I can see the stability argument as well, weight low is certainly better than high. I'm sorry I haven't been able to comment much on the Moth, I know I said I would lend a hand where possible, but I've been somewhat pre-occupied in the last few days, so I've only really had time for the I14, and a few other bits and pieces. When I have more time in July I'll be able to dedicate more time to both these projects.

Cheers,

Tim B.

 

Tim,
No weight data on the hull or sole yet. I feel (and it's just a hunch) that by the time you add buoyancy tanks or bladders and attachments to the sides of your un-soled boat, you will still be about the same weight as mine. This is just an opinion, and a pretty biased one at that ;-)
I have always preferred the open-to-the-world self-bailing transom, and would not worry about sailing backwards (;-P) or standing in the stern as possible sources of flooding. These are not going to affect anything when moving except in _reallllyyyy_ light winds in one of these things. To save some weight, I would suggest having a flat panel sole, that just goes out to the hull and stops there, without the built-in buoyancy that myine shows. You might save a little. I am not familiar with laminate schedules on these beast, and will have to read up a bit.
Steve

 

Um yeah, ignoring the cockpit sole for a moment, did you draw the yacht on Rhino v2 or 3? problem is that I'm running Rhino v 1, which is claiming that there are no objects present. It appears that the ZIP file downloaded OK. Could you see if there is a version compatability option, or failing that, just post it as a farily universal format, 3ds (not 3ds Max) is fine for example.

Cheers,

Tim B.

 

Saildesign and others here is my rant...

sail, Had a look at your model, Coming along nicely.

Are you allowed to drop the buoyancy tanks P&S. Perhaps raising the sole a little to compensate for the lost buoyancy and overall stiffness. (You also get a side stiffener.) A little artistic license with some foam will improve the comfor to the skpper.
Stiffeness across the transom could be with a light tube across the top.

Also why the swing board and not a dagger? I might be crossing some rules but I thought they were prety similar to the Australian 14. (I belive both classes have accommodated each other?)

Open transoms are they way to go. Nothing worse than waiting 5 min for water to leave the boat after a capsize when it could be gone in seconds. They are the norm for skiffs, ns14 etc out here (Even moths - Never seen ones like the pics here though)

Forget the stability issue of lower decks. With the enormous rigs on some of the skiffs out here. they don't stand up on their own anyway. Your biggest stabilityfactor is crew weight and the abillity of the crew to balance the boat.

Probably have more to say as you guys keep it coming..

luv brett

 

Tim, Rhino version 2. Send me your email addie (saildesign@aol.com) and I'll cut it in V1 and send it over.

Brett - There doesn't seem to be any requirement for _where_ you place the ballast, but it helps to stiffen the sides. As far as transom stiffness is concerned, why bother? The rudder is hung from a "thingy" on centreline. (I know there's a word for the danged thing, btu I disremember it at present - old age...)
The centreboard (as opposed to the dagger board, allows the pole to be retracted on centreline without interfering with the board, and also allows for some adjustment ot balance while underway. Yes, you could build a daggerboard trunk to have some latitude, but then you have to stop the little fountain...
Do the Aussie 14's favour daggerboards?
Open transoms - I'm with you there. ;-)

Steve

 

Ahem - under "ballast" in the post above, read "buoyancy"......
I have _got_ to find a Fountain of Youth (or something similar) really soon!

 

Steve,
I wasn't thinking about the strength of the rudder "thingy" but more along the lines of stiffening the topsides like a transom does. "Thingies" work well.

I have never seen a skiff here that has a swing board. I sailed on an 18' skiff for a year or so and never noticed the "fountain" to be a problem. Do you need to retract the pole? Is that absolutely required?

Brett

 

Just a thought - you can still retract with a dagger board.

 

Brett,
I wasn't worried about the strength of the "thingy" either, but wondering if the topsides aft _needed_ stiffening if the pedestal (that's the word for a "thingy") was there. What would make the topsides flop that much...?
Good news about the fountain, but "Yes", the pole does need to be retracted, Rule 13 (ii) says "In its retracted position, the spinnaker pole shall not extend more than 900mm in front of the foremost vertical or transverse extension of the bow. The spinnaker pole shall be in its retracted position whenever the spinnaker is not in use."
By the tme you retract a 2743mm pole according to the rule above, you still have 1843mm "inside" the boat, which is only 4267mm long, putting the aft end of the pole at 43% aft.
Yeah - I suppose that could work, but I just liked the centreboard better ;-)

Steve

 

A comment on boats that sink by the stern and those that cannot be made stable in the static condition (i.e. in irons): such boats are to some extent the equivalent of a "sinker board" in sailboarding. Perhaps I, too, am in need of an elixer of youth, but I prefer a boat that can be made to float upright even when not underway. I may design & build my Moth with a cockpit sole, but also intend to feature a transom with freeing ports and non-return flaps if I think I can build a minimum weight boat with these features. My design will be slightly wider at the waterline than the Mistrals, and I'm going to keep the rig as light as I can.

Like Steve B. I'm contemplating the use of a centerboard because I want to locate my mast & board farther aft than on other Moths, and a daggarboard threatens to be in my way or to catch on the boom vang in a jibe.

That's my current thinking, but it's not immutable. Commentary is welcome!

 

Steve,

I was thinking that the topsides need to be stiff enough for two crew to stand on. Hence replacing the "seat" with a post at the transom.

I hope you don't mind but I borrowed you sails and put them on another model. I don't intend to do a dinghy but something else I already had going got a bit of polishing. See Gallery

Brett