Boat Builder Central - Builder Forums

Ordered a used 420 class mainsail off of ebay today, so I guess I am committed to this project now

Looking at building a mast for it possibly before spring and then have the plans finalized for beams and outriggers by spring with all supplies ordered to start as soon as epoxy curing temperatures start.
My rough idea is a 10-12ish ft total beam and roughly 200lbs flotation from each of the 12ft long outriggers made from 1 sheet of 4mm apiece.
Not sure if the box beams will be plywood or 1x4s, the advantage of the 1x4s is I could get them in 12ft sticks and not need any splicing..... will have to figure it out

Still doing a little rough research on the mast but I like the basics behind this hollow one,
https://www.idniyra.org/old/articles/mast_made_easy.htm

I have never touched a sail, or even looked at one up close..... so will wait till it is here and I can touch and look at it to make sure my head is fully wrapped around the luff track and dimensions of the boltrope etc....
I think I may modify the idea I linked a little in making it slightly wider at the trailing edge and using pex tubing embedded a little deeper, wrapping the whole thing in glass then cutting the groove on my table saw.

I talked to the park historian here and even though we live on a huge 60 mile long lake he doesn't have any record of sailing taking place, he has pictures of some old Bristol Bay double enders modified with engines, but none with masts or sails (showing in the picture). He assumes that there may have been some small primitive sailing on canoes but again no actual records showing it. All kind of interesting considering how big a body of water we live on.

Cool project Narfi!!!! Jeff

The sail got delivered yesterday, the red stripe looks like it will match his canoe pretty well, so a red and white canoe with a matching red and white sail will look pretty sharp


The bolt rope goes along the full leading edge(luff) and the foot has no bolt rope but a track slug(is that the right term?)  at the clew. So even though it looks like it only needs it toward the end, I will probably build the boom identical to the mast with a track built in.

I didn't have time yesterday to take measurements on the slugs and boltrope, but when I have time I will measure and come up with some sample track ideas to test with it.

It looks like the 420 uses spreaders on the mast, is there any need for that if anchoring the shrouds further out(out at the outriggers instead of close in like the 420 dinghy has)?It seems the simplest would be to have 2 shrouds and 2 stays all to the top of the mast and anchored furthest out in each direction. Am I missing something obvious?

Playing around with shapes and sizes and configurations in solidworks, self teaching as I go. I have a student license 'free' with my EAA membership and always intend to learn more and do more with it but always end up faking it when I actually want to do something productive I can use it to get myself good 2d panel shapes from my 3d hulls which is probably all I will use it for other than rough 'looks' of everything sitting together. I figured out how to get the curved panels dimensioned out where I can read and trace them on plywood which is good enough for me, from there it will be easy to cut out and stitch everything together just like I did my other boats designed by people who actually knew what they were doing.

Nice sail!!! Jeff

As regards the shroud placement, wider would be better if you have a strong place to tie to. I wonder if the outriggers will be that place.

All sails have a center of effort that will give you the best place to position the mast, which will greatly influence performance, especially when sailing upwind. When I was playing with all this for the cedar strip canoe, I had the sail made for the boat and the mast position (just behind the forward seat). You might ask the manufacturer where that is on that sail before you decide where the mast goes.

Here's a quick read on the topic. There are lots of others....

https://www.northsails.com/sailing/en/2 ... -sail-plan

It is a 420 class mainsail. That class has pretty strict regulations on size and dimensions etc......
https://www.sailing.org/tools/documents ... 22945].pdf

I over thought weight and balance and placement in my fs17, so with this being so much smaller I was planning on a 'looks good' approach knowing that if I had a big breakfast that morning it will change everything anyways. (of course it should be close to start with)
My thought was also behind the front seat, well actually the crossbeam just behind the front seat with the mast up against it. I will take more measurements and calculations in the spring when I can dig the canoe out from under the shed (we finally have snow here!)
I know I moved the seats from the original HC14 plans, but cant remember exactly which direction or by how much so will need to get actual measurements off of it.

I started making a test sample for the mast and boom last night.
This is the two halves just sitting against each other, I need to plain the inside joining surfaces flush with each other and route the track groove in before flying them together. I don't have any wood flour left so just used some fairing mix to thicken it for the test samples.
It's 1x4 sides(3/4x3.5) and the angles are each 1/2 of a ripped 1x4.

Once it is all carved down and shaped should be roughly a 3x4 airfoil shape..... Not sure why that is better than a simple box, but does make the track easier I guess.

I thought about this over night...

I have some concerns about needing stays/shrouds on this thing...

1. The stays/shrouds will put a lot of downward pressure on the keel seam under the mast and a lot of upward pressure on the thwarts (or wherever you decide to attach them).
2. Stays/shrouds need to be tensioned properly. That means lots of setup time.
3. Stays are kind of a performance things in little scooters. Like race performance. I think you will get MORE than enough speed and might want to consider #2 over performance.

I think I would recommend a config that uses a capturing step and a mast partner over stays/shrouds. A lot simpler.

You also need to consider the CoE of the sail for the location of the dagger/lee board. if you don't get the right balance you wind up with either a frustrating or a dangerous end state. If the CoE is behind the dagger, you wind up with "weather helm" where the boat constantly points into the wind. This is frustrating as you wind up fighting to keep her on course. If you get COE in front of the dagger you have the apposite problem... always pointing lee. The problem here is that you wind up with a serious gybe potential and an increased risk of pitchpole/bow stuffage.

All the plans I have show the CoE aligned with the keel/dagger (it is actually aligned with the "center of resistance" on the non-BBC plans, I don't see a marked point on the BBC plans).

Might be worth asking JM to weigh in on mast and dagger/lee board placement.

narfi wrote: ↑Fri Jan 29, 2021 11:29 am Once it is all carved down and shaped should be roughly a 3x4 airfoil shape..... Not sure why that is better than a simple box, but does make the track easier I guess.

the sail is a wing. Literally. The mast is the leading edge. Also literally. Performance sailing and "big boats" really need shaping to reduce the turbulence of the transition from mast to sail. If you use a rotating mast the "best shape" changes to a lower profile. At the same time, a rotating mast can be less "profiled" with less impact as the sail can be shaped to reduce the impact of the turbulence.

It's all theory. Since you're not racing I wouldn't get too hung up on it. I might suggest a simple round mast with a lashed on sail as the simplest to get you started.

I've done a bit of reading on sail performance lately