Breeding Two Boats . . .

I am humbly seeking the collective wisdom of all those gathered here.

I have an old Sunfish with a hull that is beyond any repairs that I want to attempt.
However the sail, mast, spars, and tiller are all in serviceable condition (for recreational purposes).

I recently acquired a free Escape Mambo hull. It had no sail, mast, boom, or rudder. It did have the attached swing down daggerboard. They are no longer making the Escape line of boats and there are no mast or boom assemblies to be found in the US. You can still get some other parts.

Being made by the same parent company, the Sunfish rudder fits the Mambo perfectly.

I am trying to use the Sunfish sail on the Mambo.

I have modified the Mambo slightly to accept the mast and also slightly modified the Sunfish mast to fit properly to the Mambo hull. All of that is working well. I believe the Mambo originally had a 64 sq.ft. sail and, if I'm not mistaken, the Sunfish is 75 sq.ft.

My problem is how far back the Sunfish sail sits on the boat (see pictures). The boom is hanging out over the stern about 4 feet. I have only taken this boat out a couple of times and have only experienced light to moderate winds. In moderate winds it performs very well and is a lot of fun; I expect that it would also do well in stronger winds. However, I am having trouble in lighter winds. It feels like I have no control. It feels like because there is so much sail to the rear of the boat that it is pushing the rear of the boat around in light winds. The boat also slides sideways in light winds.

The other problem is that when the boat is in the water and unrigged I have a lot of sail and spars sitting in the water which become a bit heavy to hoist out to get underway.

I'm not sure if I'm making sense with all of this.

I would love to be able to find an Escape sail, mast, etc. to do this the right way. But I don't think that is going to happen. Financially, I am not able to do much of anything.

In the pictures you will notice that I have the sail adjusted quite high. I really don't like having to duck very much under the boom when sailing.

Can anyone suggest anything to help?

 

There is a way to determine where the mast goes. The type of sail used, in your case lateen from the Sunfish, creates a CE or "center of effort" a certain distance back from the mast at a certain height above the water.
The CE of the Sunfish then gets compared to the CE of the Escape. If it's close, no worries. If there's a substantial difference there might be a weather or lee helm depending on the center of effort of the new sail being either ahead or abaft the other sail.
Frankly, if the square footage of the sails are similar, the chance of a good CE matchup is really good. I'd simply try the sail out and see how you like it. Modifying the boat to adjust preferences would include angling the mast to bring the CE back to the same location as the original Escape. Other mods could be done also, but it's really doubtful you'd need to go that far. For example, moving the mast socket forward or angling the daggerboard forward or, more likely, aft to balance the sailplan.
All this is likely more technical than necessary to solve the problem. Google "finding center of effort of sail" and you'll see how simple finding the CE is. The lateen will tend to be further back than a sail that goes to the masthead (bermudan rig). The question is, will that difference matter. If so, it will manifest as a hard-mouthed helm, where you are angling the rudder more than necessary just to go straight. This will slow the boat, potentially quite a bit. A little rudder angle, up to maybe 10 degrees in moderate conditions, is normal. More and it starts to affect performance.

 

Here are a couple of photos of the two boats your working with. The sunfish's larger rig is going to draw the center of effort of the sail too far aft when it is placed on the Escape hull. In very light airs you say that the back of the boat gets pushed around, but on days with more wind the boat handle ok. This all make perfect sense.

With light airs, the boat is not moving well and foils in the water are not working well yet. When this is happening, the imbalance in your sail rig is going to over power your water appendages. As the winds pick up, the foils (rudder and centerboard) start to work and they can provide enough resistance to the sail forces for the boat to behave properly. I suspect that on a really windy day, the imbalance in the rig will show itself with some strong weather helm. Most likely, to get the rig into balance the sail will need to be shifted forward or the centerboard shifted aft, or both.

 

Cut the sail and resew the edge. It is not a racing sail so it will perform well enough. The aluminum pipes can be easily cut and sanded smooth.

 

In the pictures the mast is angled aft and the sail is tilted back to horizontal. If you had a mast forward and tilted vertical you might be able to use the sail as is. Lowering the sail by moving the mount point up on the upper yard also moves the sail forward. Shortening the foot of the sail would move the center forward but you seem to like the large sail.

A silly but possibly the best solution is to just make a new deeper larger rudder. More sail requires more lateral resistance and a big high performance rudder would be the quickest most effective way to get it. The idea that a sailboat needs a little rudder balancing a big keel is unimportant on such a small boat.

 

One of the best things about the Sunfish rig, and la teen rigs in general, is that they can be tuned a great deal just by where you tie the halyard and where you put the goose neck. Racing Sunfish sailors have the ab9lity to loosen the goose neck clamp and move it fore and aft between races. This is one of the big deals. If yo play around with these two variables, you can make it so the tack of the sail is quite close t the deck, yet the boom is angled up so you can get under it easily. This will also move the CE of the sail further forward. It is not uncommon for 'fish that have been raced to have scratches in the foredeck from where the gaff and boom have rubbed back and forth.
Some information about this from Eduardo Cordero:
106"-107" measured upwards on the upper spar starting at the point where the black cap meets the upper spar on the bottom. Lowering halyard location raises the height of the boom above the deck. This adds power to the sail. Increasing the distance from the bottom to the halyard location will do the opposite. Make sure the line does not slip. Apply electrical tape on top of it.


* In light air, do not over tighten the halyard because it may cause the mast to twist.


Head location:

Measure 160" on the upper spar starting at the point where the black cap meets the spar on the bottom and tie the head of the sail in this position. Keep the luff loose, so you have power for sailing downwind, especially in light air.
Gooseneck: You can set the gooseneck between 12" and 22" but I recommend starting at 14" or 16” from the point where the black cap meets the boom at the front.
SHC