CrabClaw / Lateen model boat

Hi

I have been put in charge of designing the sails of a rc boat for a club.
We are only allowed 2 servos which is quite limiting.
I would like to do something a bit different not just bermuda rig and was looking into the lateen and crab claw sails.
If you could give me any advice that would be greatly appreciated.

The hull has to be a monohull to comply with the rules of the race.
Other boats have failed in the past because they have fallen apart or become unstable so we would like ours to be pretty stable.

Im sorry if this is a bit unconventional but i didnt know anywhere I could go to get help.
The max mast/ rig height is 90cm
max length is 70cm
max sail area is 2000cm2 (which seems very limited)

Thx in advance

Alex.

 

Alex;
The RC boat you describe is rather small compared to popular classes, unless you consider the "Footie" that some of the Aussies fancy ( one foot long or 30.5 cm.)
The rig size and height are reasonable for a boat of your specified length.

I have numerous experimental RC boats, some of whom are rigged with odd sailplans. The following comments are the result of that experimentation. Keep in mind that model boats have different requirements and consideration than full sized boats in which the sailor does the controlling.

When you design your sail plan you should first consider what the boat is to do. I will make a presumption that the interested parties will race the boats around a closed course. In that case much of your time will be spent going to windward. It seems obvious that the rig should then be reasonably efficient on windward legs.

Neither the lateen nor the crab claw is particularly good going in that direction. If you want to be different you can try a lug rig or a gunter. The gunter is generally better to windward and quite efficient off the wind as well. The lug is powerful off the wind. It does put a lot of area up high which will tend to burden the boat in anything but running conditions. When running the Lug will tend to stagger (death roll).

I suggest that a good start might be a swing rig. In case you are not familiar with that type; the boom does not rotate around the mast. It is fixed in such a way that the boom can swing up or down but not rotate around the mast. The sail is trimmed by allowing the entire mast to rotate. Let the boom extend forward of the mast some distance, perhaps half to three quarter the distance of the rearward boom extension. The jib is tacked to the forward extension of the boom. Jib stay tension then becomes functional as a boom vang (kicking strap). The jib may be either loose footed or club footed. The main is attached in the normal way. If you want to be a bit more exotic with this rig you can cut the top of the main off so that the top is flat. The main now looks a bit like a flat headed gaff sail. You will need a way to control twist in the upper part of the main. Do so by using a horizontal extension at the mast head. A mast crane like fixed appendage to the mast.

The advantage of the swing rig is three fold. One: the jib counters the force on the main and unloads the sheet servo. You can use a smaller than usual servo in that case. Two: Rigging the boat now becomes as easy and quick as it gets. Just stick the mast in the hole and hook up the mainsheet. No wire, no complications. With this rig you can even tune the rig before you get to the pond. Actually that is kind of fun on rainy nights. Three: you can easily change the balance of the rig by tacking the jib down at different places along the forward boom extension.

I hope this gives you some ideas

Gene

 

Thanks for the info. We actually entered last year witha swing rig bermuda design. It wasnt very well executed though as it was rushed whole boat designed and made in about 2 weeks in our lunch breaks
We ahev 3 teams this year. one is going to make a swing rig. I will certainly pass on your advice. I have decided to try a soft wing sail. And the other team is making a good old bermuda. Well made and efficient.
So we get the best of all worlds.
Have you ever tried putting solar panels on the decks. This should power the servos right? or at least extend run times. As my design will be directly linked to the mast which will require quite high power.

 

Alex;
I have not tried solar panels. They are too heavy for a model boat and particularly for the small one that you describe. The capacity to generate current is a function of time and exposure to suitable light. A small solar cell will not produce enough current to charge your battery meaningfully. Perhaps it would do so within a few days but not during the hour or two when you might be sailing.

The wing sail does not require great sheeting power. Consider the location of the mast pivot point. Moving the pivot point aft will tend toward balancing the forces on the whole rig. You must not over do it though. The wing sail is a real dog if the mast is not rotated just so.

Wing sails are also a very narrow groove sails. That is to say that most wing sail arrangements are very sensitive to trim angle. Use some "woolies" or streamers and watch them carefully. These things will stall at the slightest provocation. If you can get the wing thing dialed in right, it is a very powerful rig. Generally speaking simplicity is a better way to go. Model sailing is a different deal because the skipper can not feel the boat, he just has to see the boat. It's dificult to anticipate and react to small shifts while sailing in your full sized boat. Playing shifts with a model boat that may be 100 meters away is extremely dificult. Best to have a simple rig that is reasonably forgiving and pay attention to tactics rather than focusing on delicate sail trim.

O.K. if you must tinker with something novel, consider a cat yawl rig and no rudder on the boat. Steer with the jigger sail. Advantage; Less wetted surface and appendage drag. One servo for the main and one for the jigger. This works very well on all points of sailing except running, when steering gets a little tricky.

Gene

 

Alex, I don't know anything about RC boats, but I do know that Latin sails are popular in Canarias, Catalunya and Italy.

They race real boats and also RC models.

Look at this site, under "Inicio" and under "Vela Latina", you are going to find lots of information about latin sail RC models .

http://clik.to/modelismonaval

This is one of the race boats (not a model):