J Class Endeavour


Been working on the “Park Avenue Boom” for my 1/22 Scale Endeavour.
The original boom was almost 4.5 feet wide on its flat top surface.
Triangular in section, widest and deepest in its mid length.

Along the flat top of the boom were tracks running from side to side, these had stops fitted to them, to enable the shape of the Foot of the mainsail to be set to suit the prevailing conditions.
This gave the mainsail an “End plate”, to stop the air from spilling out at the bottom, very similar to the “Winglets” now seen on many Airliners.

Of course many of these new booms suffered breakages, but it was a big advantage to have one fitted at the time, no carbon fibre in 1932 !!.

My model boom has a carbon fibe tube, with triangle formers and a ply outer skin, trying to make it as strong as possible, yet keeping the weight down, the weight is winning at the moment !.
Taken a few photos, will post them as soon as possible.

John. :slight_smile:

Interesting - looking forward to seeing your depiction of it. I’d certainly hate to get whacked in the head by that monster while on a tack. :scared:

There’s a spar worthy of the name BOOM! :slight_smile:
Do we get any production pics - I love watching the building process.


This is where I am up to with the Boom construction.

It is built onto two tapered Carbon tubes, joined in the middle with a wooden dowel.
The triangular frames were fitted on from each end, so there would be no mix ups because of the shape of the boom.
A bit like bulkheads on a hull, each one is different from the others.

The tubes were then set up on Vee blocks and the top surface was drawn on.
Using the same setup, the top surface was placed vertical and a centre line was drawn on each frame.
The width of each frames was marked onto the tops, then the depth of each frame was marked onto the centre lines of each frame.
Each frame was labeled to keep its position on the tube when taken apart for cutting.

Sounds easy now. but it took a whole lot of thinking about to do it!!!.
Watch this Space!.

John. :wink: :wink:

1:20 J class is on my list of “builds to do” so it would be good to see more on your project.

Regarding the PA boom, curious as to why you taken the approach of building around a tubular spar. Given the boom is essentially a flat sided structure I cant help thinking that you would get a stronger and lighter boom if you built a simple male plug and moulded over it in CF? I would probably use a blue foam plug and then disolve it out afterwards. Just a thought.


Hello Ray,

Good idea, a Carbon moulded boom, but the finished structure would be hollow, with no way into it, how then to fit attachments to it for the Main sail, Main sheet, and the Vang???.

Using a Carbon tube, I have a strong section which now has all the fittings in place, made with Piano Wire epoxied in position.
Where the fitting are, the carbon tube has been reinforced with another piece of Carbon tube and wooden braces added.

The forces on a J Class boat are enormous, trying to keep things “Scale” and strong enough are a BIG problem !.

John. :wink:

John, the way I would deal with fitting the sort of attachments you mention would be to embed small blocks of tufnol into the right places on the foam core, laminate over it and then drill and tap into the tufnol blocks for the fittings.

Are you going to have sail shape control using the slider concept of the original?

I’m not sure that your boom won’t twist under load.

BTW, lamiinating over this sort of shape, i.e. akin to a shaft, is much easier if you use ‘kniited’ carbon fibres tubes. These expand/contract to a rerasonable degree and are available as un-directional and bi-axial, which mixed together will give a strong, stiff and light boom. You just slide them over the core and wet it out and you can easily lay up several layers in the same exercise. Ideally I would vacuum bag the whole thing while its is curing but if you haven’t access to that you can get heat shrink tubing that will keep the laminate consolidated, especially around the corners of the triangular section.


John, just had a quick look at your website - like the schooner - did you build the Endaevour hull?


Hello Ray.

The Endeavour is built onto an old 10 Rater hull, very near scale above the waterline, but below it is a large bulb keel, not seen while sailing - - just like the Schooner!.
Scale hulls, especially Scale under the waterline, can be restricted to light winds, which certainly does NOT apply to the Schooner.
Endeavour is much the same, sailing in high winds no trouble at all, only got the one set of sails, so its sail, or go Home !.

The Retired Engineer in me says the boom will not twist!, it is to be clad in 1/16th Ply, the attachment points come out though the ply - -no way it will twist.

If the sail control slides can be made strong and small enough, they will be fitted, maybe I can compromise on strong/small, will have to see about that.

Never used Carbon layups, didnt want to risk using it on an important part like a Boom.
Done loads of work with Glass Fibre, but no Carbon - - - - yet !!.
Got the top of the boom fitted and cut to shape, now to make the sides.

John. :slight_smile:

John, if you’ve worked with glass then you can do carbon, working practice is just the same.

I’m assebling a vacuum bagging setup at the moment and one of the first things I’ll be using it on will be the swing rig booms for my 2metre cat.

Anyway, now here is something really weird, check out the images below: this is my semi-scale Rainbow project. It is built on an old 10rater hull (actually Red Herring) that has lines that are close to Rainbow above the waterline… Its a bit of a slow study and takes a distinctly second place to the multihulls. I’ve built it to have control of two loose-footed headsails. I’ll take a couple more pictures of where it is today.

Eventually I intend building a scale 1:20 J, both above and below the waterline though I may compromise by deepening the draught as with the US model J class. Have you seen the hulls that Larry Ludwig sells?


Hello Ray,

Yes, I have often drooled over Larry’s hulls, but they are BIG!, 1/16th Scale,
So even with an Estate car,they will be a squeeze to move around.
There are some pictures of 1/10th Scale J boats at this site in France


Now that IS BIG !!.
The boat is the J that has been restored, used to be J K4, I think they have ruined it by fitting all those winches on the deck, the original boat only had “Rowing Winches”, there are photos to prove this.
The present boat looks like a christmas tree with over 20 winches on the deck ---- there are only 3 sails !!!.


the winches are there more for when they are not racing, cruising with charter guests / owner, and the crew is much smaller and i would imagine they are running a one line one winch system, extreme boats like the modern J’s (which endeavor is now) do have a lot of ropes. having said all that there are a lot of winches, a lot of serious detail, a very impressive model.


Here is a photo of where I am up to with the Park Avenue Boom.
The top of the boom and one side are shown, with the third side ready to be attached.
The third side will be made flush with the others, a radius put onto the edges and then the Mast pivot will be fitted.
The end on the boom has a small curved block to seal the end.

Have thought long and hard about fitting the sliders onto the top surface of the boom - - - the sail control slides - - but I dont think they can be made to scale and still be strong enough.
The boom has taken a lot of making and leaving off the sliders is a big no, no!.
I will stop work on it for a couple of days and give it some more thinking about !!!.


Hi John, I finally got round to taking a couple og pictures of my near-scale J class Rainbow, still a work in progress…

As noted earlier, the boat is based on an old 10rater fibregalss hull that I picked up for a tenner at a car boot sail - it had never been touched except to remove the ‘canoe’ stern from the hull moulding.

The next job I’m planning is to finish decking it; the deck in the pictures is a sub-deck that will have a lot more removed. because the deck houses on J boats provide only very small openings to access servos etc. I’m planning to have another deck that will be completely removable. Still working out the how though.

I’ve built it to have twin headsails; I’ll use three winches, one to shhet the mainsail, one to sheet the headsails and one to tack the headsails.

As you can see, it has a mast almost finished. I bult this from hardwood sections, planed to the right ‘aerofoil’ section, and incorporated a groove in the back for the mainsail luff and a hollow channel down the middle for the mast hoist line. To stiffen and strengthne it I’ve wrapped the front three quarters in carbon fibre tape and the bottom few inches in carbon fibre ‘sock’. It seems quite strong and should be fine when its fully braced with shrouds and spreaders.

Anyway, here are some pictures.


Someone posted this on another forum - lovely isn’t she? And the boat’s really nice too!

Hello Jerry,

Now then, what size sail winch would that need???.
With all that sail area it would HAVE to be big, possibly with a V8 engine !!!.
Moving it around must be a nightmare too.

I consider my boats to be big, but it seems they are not !!.


That hull is for sale right now on flebay Weight is about 100 pounds. My guess for a servo winch would be one of Servo Citys robotzone servos found here.

I just installed one on my Newport 12, and that doesnt even come close to the size of that J Boat in pic above.

If it were some other rig, a ship, brig, schooner, lugger, dhow, etc it would be different, but it’s just a Marconi sloop - you might as well get yourself a nice day sailer that you and some others can get in.


JUST found a fairly clear, black and white 1930s photo of the Sail setting slides, the REAL things!!, missed it earlier, but, just now it jumped out at me !!.
So now I have an idea what the sliders looked like, I can start on drawing up a Scale version of them.
Things are starting to look up!.



Here is a pictorial of the sail control tracks, sizes still to be finalised, but the width of the track has to be about 5mm !!.
The length changes to suit the position of the track on the Boom, so they are nearly all different lengths.