DTFB Racing Sloop- Scratchbuilt Sailboat

[Crawford Bros. Aeroplanes]

I've had this idea bouncing around in the back of my head for a while now and finally decided to start on it. I've seen a few guys build boats out of DTFB and even cardboard and it seems to work better than you'd expect as long as it's sealed tight. Usually some thick coats of the right paint is enough.

RC sailing has interested me for a long time. When I was a kid I liked watching the old men sail their handcrafted boats at a park I lived by. After a bit of research on the internet I stumbled across a popular design by Tippecanoe Boats called the T-series. Tippecanoe makes this design in a few different sizes with the most popular being the 37" T37. It's a beautiful balsa-hulled design that's remarkably lightweight, leading to good well-rounded performance.

One of the things I liked most about this design was how simple the hull is. It's only 4 panels in total, the keel is flat-bottomed and the deck is straight. Clearly very easy to build in foam board. 37" is an odd size for DTFB so I scaled it down to 29, a nice midpoint between the full-size T37 and the travel-size T27. After only an hour or two I had a decent hull finished.

On its side, showing the flat keel:

I didn't get an pics before I took it out to the shop but I also fabricated the rudder. I used 1/8" balsa for the core and set a piece of 1/8" welding rod as the shaft. I then laminated a piece of cardstock on either side and sanded it into an airfoil. It's currently drying after being sealed with epoxy resin.

For the rigging and running gear I'm using some dowels and balsa that I'm sharing with my other boat project. Sails will probably be cotton, I may use a bedsheet I brought back from MCRD. It's their fault, they issued me two.

 

[synjin]

If there are any construction sites near you could pick up a piece of Tyvek for the sail. Fighter kite home builders like Tyvek for their sails.

 

[Crawford Bros. Aeroplanes]

If there are any construction sites near you could pick up a piece of Tyvek for the sail. Fighter kite home builders like Tyvek for their sails.

I'll look into it, I'm trying to keep costs as low as possible though

 

[Crawford Bros. Aeroplanes]

Rudder is finished and sealed with epoxy resin.

 

[Monte.C]

I'm starting to get jealous.

 

[Crawford Bros. Aeroplanes]

I'm starting to get jealous.

Why? This is the "build it yourself" forum, just build your own. We could do a group build.

 

[Monte.C]

Oh believe it or not I don't have a good place to sail. All the ponds here are in city parks, and they'll likely chase you away. I could shoot in that direction and maybe get away with it because it's quiet, slow & cute, but I'd rather fly right now. I can still be jealous if I want to! That example you show is so beautiful. They don't really leave it with an open hatch do they? Anyway I'm still offering any sailing advice you might need.


for a small fee.

 

[synjin]

Tyvek is the material that they wrap around the outside of houses during construction as a vapor barrier. It’s like a fiber filled plastic. You can wash it, and you can paint it. I’ve even seen some small scale skiff homebuilders use Tyvek as sails. At most construction sites there will be a bunch of cut-offs that the contractors are throwing away. They used to make the Priority Mail envelopes out of Tyvek as well. Of course, a heavier weight plastic painters dropcloth would make a good sail for that size of boat. You’d have to do a few darts along the leading edge of the sail to get the airfoil shape started regardless of what material you choose to use. Using plastic or Tyvek you could just use packing tape or duct tape. If you use some sort of fabric you’ll have to do some sewing.

 

[Monte.C]

Tyvek is the material that they wrap around the outside of houses during construction as a vapor barrier. It’s like a fiber filled plastic. You can wash it, and you can paint it. I’ve even seen some small scale skiff homebuilders use Tyvek as sails. At most construction sites there will be a bunch of cut-offs that the contractors are throwing away. They used to make the Priority Mail envelopes out of Tyvek as well. Of course, a heavier weight plastic painters dropcloth would make a good sail for that size of boat. You’d have to do a few darts along the leading edge of the sail to get the airfoil shape started regardless of what material you choose to use. Using plastic or Tyvek you could just use packing tape or duct tape. If you use some sort of fabric you’ll have to do some sewing.

Good ideas.

I don't ever remember darts sewn into sails. I used to fold a sail on the floor of a big room with my dad and the sail was perfectly flat.
We DID have battens in the leech - the trailing edge of the sail - so the back edge remained quite flat compared to the luff - the leading edge.

 

[Monte.C]

Looking at the sample pic once more -
I believe I know what's happening here.
It's a flat sail. The boom vang - the lines tied at an angle between the lowest part of the mast and the boom - has got tension on it, as it should. This pulls the boom down close to the mast, thus pulling tension on the sail along the mast. That back line that goes from the deck to the top of the mast - I forget what it's called - that pulls the top of the mast astern. Now the mast has a slight bow in it. Your mainsheet pulls the boom down where it's needed most: When you're "pointing" close to the wind and you have the sail pulled in tight, nearly to the boat's centerline. The mainsheet doesn't have this downward effect on the boom very much when the sail's further out, on a reach or sailing downwind.

Between all these forces, that's why you see a bit of luff at the front edge of the sail in the pic. That luff will fill when you sail it right.

 

[Monte.C]

I forgot the downhaul. This runs right along the mast between the deck and the boom, and pulls the boom straight down at the mast, and puts tension on the sail. Then the boom vang is at an angle of around 45 degrees to the boom - looks like they're using a turnbuckle here - pulls the boom into a slight bow, tensioning the sail across its entire surface.

 

[Monte.C]

It is possible that for RC models, for some sail material and some smaller size boats they might be pre-shaping a sail. I don't know the answer to that. I've just never heard of it in full-sized boats.

 

[Crawford Bros. Aeroplanes]

That pic is the "racing upgrade" version with some different rigging and full cf spars. Here are some pics of the "basic" version. Notice there's no vang, the backstay (that's the word you were looking for) and sheets are still present. There also appears to be darts sown into the trailing edge of the mainsail?
I like the idea of the tensioned mast and flat sails, I'm just not sure how to figure out the proper tension for the vang and backstay.

 

[Monte.C]

That pic is the "racing upgrade" version with some different rigging and full cf spars. Here are some pics of the "basic" version. Notice there's no vang, the backstay (that's the word you were looking for) and sheets are still present. There also appears to be darts sown into the trailing edge of the mainsail?
I like the idea of the tensioned mast and flat sails, I'm just not sure how to figure out the proper tension for the vang and backstay.

View attachment 186672

View attachment 186673

Those straight bits are battens. Straight, fairly stiff rods slotted into sewn pockets in the sail. For models I would hope there's a way to glue or sew them right to the sail. (?) I wouldn't want to make it so complicated that I'm trying to sew a 6cm wide pocket in the sail.

For the boom vang, don't worry about it. Just put a bit of tension on it and it'll be fine, For these little models it seems to me a turnbuckle would be the only way to go, I guess.

The backstay? Pretty much the same thing. Put a bit of tension on it so you can just see the mast arc a tiny bit, and see where that takes you. Everything can be adjusted later.

Oh that's what I thought, they're taping a piece of Plexiglas to the deck for a hatch.

 

[Monte.C]

See, if you didn't have a vang, when going downwind, with your sail all the way out, the boom would rise and the sail would balloon out like crazy. Something you don't want.

 

[Crawford Bros. Aeroplanes]

Those straight bits are battens. Straight, fairly stiff rods slotted into sewn pockets in the sail. For models I would hope there's a way to glue or sew them right to the sail. (?) I wouldn't want to make it so complicated that I'm trying to sew a 6cm wide pocket in the sail.

For the boom vang, don't worry about it. Just put a bit of tension on it and it'll be fine, For these little models it seems to me a turnbuckle would be the only way to go, I guess.

The backstay? Pretty much the same thing. Put a bit of tension on it so you can just see the mast arc a tiny bit, and see where that takes you. Everything can be adjusted later.

Oh that's what I thought, they're taping a piece of Plexiglas to the deck for a hatch.

So the battens prevent flutter on sails with the leech extended further aft, i.e. the curve you see in the rear of the mainsail on those two pictures. I just realized that it's the same boat in both pics, different rigging but definitely the same hull. I really haven't seen extended leeches or battens in any other T37s leading me to believe that this one has aftermarket sails. If I did end up going that route I could probably just stitch some bbq sqewers to the sail.

I'll have to make a trip out for some brass fittings and a mast, just gotta figure out where to get turnbuckles this size. I suppose I could just use a line, after all it's a line on most full size boats. I think I'll use fishing tackle for some of it, those little clips will be perfect. I also managed to find a pic that shows the bend in the mast nicely.

 

[Monte.C]

So the battens prevent flutter on sails with the leech extended further aft, i.e. the curve you see in the rear of the mainsail on those two pictures. I just realized that it's the same boat in both pics, different rigging but definitely the same hull. I really haven't seen extended leeches or battens in any other T37s leading me to believe that this one has aftermarket sails. If I did end up going that route I could probably just stitch some bbq sqewers to the sail.

I'll have to make a trip out for some brass fittings and a mast, just gotta figure out where to get turnbuckles this size. I suppose I could just use a line, after all it's a line on most full size boats. I think I'll use fishing tackle for some of it, those little clips will be perfect. I also managed to find a pic that shows the bend in the mast nicely.

View attachment 186680

Looks good -
I'd like to see a proper boom vang on that one, it would flatten the sail better.
The battens firm up the leech and they also just give a flatter back half to the airfoil, a better airfoil shape.

 

[Monte.C]

I raced these for a while. A tiny, very slippery single-handed racing class called a Laser.



You can see the boom vang and the downhaul at the mast. There's also an outhaul at the tail end of the boom. We would tie it so it not only pulls the bottom of the sail out, but also with a wrap around the boom it would keep that corner tight down on the boom, even when you want to let the outhaul out a little bit, like when there's barely enough air to sail and you want a deeper sail, not as flat.

The mainsheet runs on what's called a traveler, it runs across the deck at the stern. I imagine you can find this on a lot of models too. That's so you can pull it down as hard as you can, like to maintain maximum speed while pointing as high as you can to the wind - you want the sail as flat as you can get it. This is so you can pull it down super flat but it's still anchored to a place toward the side of the deck instead of in the middle. As you come about the sheet slides over to the other side.

 

[Monte.C]

Wow and she's got that sheet cleat-to-cleat at the stern. She's driving hard and pointing as high as she can.

 

[Monte.C]

Oh, here the boom is fixed on a bracket right on the mast instead of loose on the mast, so instead of a regular downhaul we use the same thing but right to the sail instead of the boom.