36R model yacht information

[Gareth JonesParticipant @garethjones79649]

I have been given a bare fibre-glass hull for a 36R yacht that I would like to build as a vane steered model. I have been told the design is a Jagermeister by Martin Dovey but the design is about 30 years old and he no longer has any information on it. I have also been given a keel weight for the hull which seems to my untutored eye to be a bit on the heavy side at 3.75 kg. However it is quite nicely cast and shaped. Does anyone have any information on this design or could anyone advise me if the keel weight is likely to be correct?

Gareth

[Gareth JonesParticipant @garethjones79649]

[Malcolm FraryParticipant @malcolmfrary95515]

36R boats, as I remember, had no restrictions on sail carried, but did have restrictions on depth. A big weight is correct. A strong carrying handle on deck will be in order, or something that will do the same job under a deck hatch.

[Gareth JonesParticipant @garethjones79649]

Thanks for that Malcolm,

There are no limits on displacement or sail area for a 36R, although there used to be a max weight of 12 lb. On that basis a keel weight of about 8.4 lb seems a lot. However I guess the 36R is only a little bit smaller than a one metre yacht, has a shorter keel and usually carries a comparable sail area so maybe it does normally have a heavier keel weight to compensate.

I am going to stick the hull in the bath with the keel weight inside and see where the waterline sits, pending anybody coming up with more detailed advice.

Gareth

[Malcolm FraryParticipant @malcolmfrary95515]

As I recall the rules, the hull complete with fin and weight had to fit in a box with internal dimensions of 36" X 11" X 9". Shallow draught, big sails, lot of weight needed. Because there is a link betwen sail area and requires area of the fin, a shorter (vertically) fin needs to more horizontal length. This in turn means that it will tend to run straight more readily, and the consequence it the need for more rudder. One thing leads to another, "great aches from little toe corns spring" to misquote someone.

This would effectively give a practical maximum weight because of the shape that would fit and still be a boat. I never did know whether the height or beam had the 11" limit. I nearly bought a second hand one at Ellesmere a couple of years ago, but got talking to a friend – when we finished chatting, it was gone. I still don't know whether he saved me £30 or cost a me bargain.

[Gareth JonesParticipant @garethjones79649]

I have tried putting the hull in our pond with the keel weight inside resting on the bottom in approximately the correct location. The water line is less than 10 mm up from the bottom of the stem and just on the bottom of the transom. Consequently I think the weight will be OK and not too heavy.

For some reason, possibly a result of changing to a Windows 10 computer, I can't seem to post photos in the portrait format any more,

One thing I think I will change is the orientation of the weight which is not circular in section but a flattened ellipse. The original builder obviously planned to fit it with the major axis of the ellipse vertical as it has a slot cut to accept the keel fin. I plan to fit it with the major axis horizontal so that the centre of gravity of the weight will be lower. and I will have to fill the slot that has already been cut with some lead sheet and resin.

On a different topic we have noticed an unusual phenomenon with our pond a couple of times in the last month. After a short period of very heavy rain, the water level in the pond has been found to be 2-3 inches lower than normal. This seems illogical at first glance but after Googling the internet there is an explanation which seems quite plausible. How many of you can work out what it is?

Gareth

[Tim RoweParticipant @timrowe83142]

Hello Gareth

It maybe an optical illusion but the boat looks slightly bow down in the top photo. With a near vertical stem the convention is more likely that the bottom of the stem just kisses the waterline.

Does the boat already have a fin? If not, what material are you going to make it from? By the time you add a fin, deck, mast, rigging sails and fittings you will have added a fair bit more weight.

I have a feeling the bulb is going to be a bit too heavy but it is easier to remove material than put it on. Lead planes easily with an ordinary smoothing using a drop of white spirit as a lubricant if necessary. A sharp Surform also rips off lead quite quickly. It will be interesting to see how you get on so please keep us informed.

I am envious of your pond. I had one when I lived in the UK but they are not very practical here is Spain unless they are completely shaded. I think your conundrum could be that your soils is heavy with clay? Am I on the right track?

Tim R

[Malcolm FraryParticipant @malcolmfrary95515]

The vertical major axis might just give a better hydrodynamic shape when mounted on the fin (reduced swirly eddies where weight meets fin). In weed conditions, it might also be better at shedding strands. This might well outweigh the advantage of the lower CoG of the weight. Or the original owner might just have found it easier to mount like that.

[Tim RoweParticipant @timrowe83142]

The best hydrodynamic shape is a perfect circle but the flattened shape looks nice and does lower the cg a bit if it is fitted as proposed. The other point is that with the major axis horizontal it forms a better "end plate" reducing tip vortices and creates small increase in projected fin area when the boat is heeled compared with a flatter keel.

The best way to reduce drag where the hull and the bulb meet the fin is to radius the join with a fillet. All this stuff though is pretty marginal in the average model but does make a difference in the competition classes.

I am intrigued Malcolm about the weed shedding characteristics. In my mind's eye the only type of keel that would shed weed would be quite raked and the bulb would be completely trailing.

Tim R

[Malcolm FraryParticipant @malcolmfrary95515]

Any bulb sticking out in front of the leading egde of the fin is a hook to grab weed. A lot of (earlier) 36 inch boats had a longer fore and aft fin to give the required area, so they could have their ballast arranged so that it didn;t poke out in front. A strand of weed sliding down the fin has a better chance of snagging the wider shelf presented when the weights major axis is horizontal than the narrower one of the vertical arrangement. Of course, any weed that gets past the fin but finds the rudder is another story altogether.

The raked fin with a trailling/faired in weight is pretty much a description of a pond yacht arrangement. I have heard that on the south coast, originating in Poole, there is a class, possibly called a "Poole 8 Metre", about 1 metre long, using IoM rigs, with such an underwater arrangement, that is or was intended for use in severely weeded water.

[Gareth JonesParticipant @garethjones79649]

Tim and Malcolm,

The hull is slightly bow down in the photo but that is easily addressed by positioning the keel weight slightly further aft. I have decided to go for the ellipse major axis horizontal to get the c of g lower. Generally there is not a weed problem in the ponds I am likely to sail it, being in mind it will be a vane steered boat rather than radio.

I am going to build the keel using the method described on the American Model Yacht Association website, as described here AMYA. Essentially it is laminated from a 1/32" ply core, sandwiched between 1/16 balsa. 2 layers of unidirectional carbon fibre and resin and a final covering layer of either carbon fibre or glass cloth and resin. The skeg and rudder will be similar.

I have several other projects on the go, either needing finishing or boats needing restoring so this one will be on the back burner for a while. However I have started looking in the scrap bin at our local B and Q for some suitable MDF or ply to build a measuring box. The requirement is the hull must fit inside a box with internal dimensions of 37 inches long, 9 inches wide and 11 inches deep. Although the class is still known as 36R, the original requirement for the hull, less the rudder to fit in a box 36 inches long has been superseded and the current requirement is for the hull including the rudder to fit in a box 37 inches long.

Gareth

[Bob Abell 2Participant @bobabell2]

Sorry to butt in like this Gareth, just letting you know that your Loch Ness Monster video, has been posted on the Website we mentioned last Sunday at Hooton Park

Thank you

Bob

[Gareth JonesParticipant @garethjones79649]

This is an update on progress on the build of my 36R model yacht.

After some thought I have made a keel to one of the designs suggested on the American Model Yachting Association website. It consists of a 1/32 ply core sandwiched between two pieces of 3/32 balsa. This was sanded to shape and then covered in two layers of unidirectional carbon fibre cloth followed by a single layer of woven carbon fibre cloth. Each layer of cloth was separately coated in Z-poxy resin before adding the next. The resulting keel seems pretty stiff.

I have made two supporting frames from 4 mm liteply which tie the keel to the sides of the hull and added a longitudinal stringer at deck level. All the parts interlock so the keel is very rigidly located and supported.

The rudder skeg was made from 4 mm ply covered in glass cloth and also locates in the longitudinal stringer. The rudder is of similar construction with a brass tube keyed to the rudder with three 1/16 brass rods as a pintle.

I made a stand which supports the hull with the waterline horizontal and the hull laterally level so that I could check the keel and skeg are both vertical and in line. The stand is just a couple of scrap pieces of 9 mm MDF, supported on a magnetic working board.

After sanding down and drilling some lightening holes the whole assembly has been glued together with Araldite. I have added a small ply plate to form the basis of the mast step.

My next task was to cut a slot in the lead keel weight to take the bottom of the fin. I worked out the C of G of the keel weight by balancing it on a round piece of dowel. I have a drawing of a similar 36R hull which showed the centre of buoyancy of the hull and assumed for the time being this is the same on my hull. I then marked the position of the slot in the ballast weight so that its Cof G will be directly below the hulls C of B.

After marking the required position of the slot I chain drilled a series of 6 mm holes about 30 mm into the ballast weight. I then fixed the ballast weight on to my workmate and using a 6 mm cutter in my router, cleaned up the slot to the full length and depth, gradually increasing the depth of cut by a couple of mm each time. This gave me a nice clean slot with no apparent damage to the cutter or router. (I carefully swept up all the bits of lead afterwards)

I have made the deck from 2 mm liteply with cutouts that will be covered in adhesive deck patches to give access to the interior and reduce weight. The deck has been given a couple of coats of Z-poxy to seal the surface but needs to be rubbed down and will be given a final coat of varnish after its glued on.

I made a mount for the vane mechanism from a piece of 1 inch wide carbon fibre strip that I found in my new desk during an office move about 30 years ago. I knew it would come in useful one day. Its very light and very stiff.

I have estimated the weight of the mast, sails and rest of the rig by weighing a Marblehead rig I have and assuming the 36R will be about 90% of the weight. A tin of salmon and packet of Oxo came close to the estimate at about 420 grms.

Next came the first bath test with the keel weight held on the bottom of the keel with tape.

Miraculously everything seems in balance so my next job is to fix the keel weight permanently

A bit more progress to report shortly.

Gareth

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