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[warspite]

I built a boat which requires a fin and bulb to remain upright, it is a sail vessel and I have a tempory 'pendulum' style solution fitted. The question is, to keep the vessel at the waterline and upright requires that the 'Pendulum' is a certain length, and the weight at the base is a specific amount, its fixing position is slightly further rearward (about 20mm) than the centre of the weight, I need and want to reduce the depth of the pendulum with a proper fin and bulb, but i do not want to create a weed catcher, the weights are not a lot (as I fitted too much weight internally and cannot remove it now to add it to the bulb and therefore reduce the fin length).
 
Is there a specific calculation/shape/design that will help, cantilever expresions etc, and materials - currently a brass tube with a brass base plate and tempory bolted galvanised washers. A fin and smaller depth will help enormously, the fin to give stability in helping to push forwards when being blown from the side.
 
I am concidering breaking into the vessel to remove the weight, but that has its own issues, total weight of the pendulum is 190g including 2x53g washers at the bottom, the vessel is really small and difficult to gain access to, I am concidering on building another to compliment it but if I can get this one to sit right and can then do this for the other as well. Sorry this is sketchy but I do not have photos of the vessel.

[tobyker]

It really is very difficult to answer this without a photo. If the problem is that the weight needs to extend further forward that the ideal fin shape, thus creating a weedcatcher, you may have either to get the mass of the weight further aft, and balance the hull fore and aft with a lump of leas in the bows, or make the fin into a plate keel so that it tapers down to the forward edge of the weight. Long keels are no bad thing - they help the vessel keep her course, though you do of course lose some manoeuverability and can't turn her on a sixpence.

[warspite]

Speed is not an issue - but stability and the ability not to collect weed  , the vessel is a square rigger, but the issue is a long 300-450mm (its in the loft for the winter) pendulum which is made from about 8mm dia brass tube, the weight of which is part of the total weight needed (refered to my notes but the dimensions are a guess without physically getting up there and is to darn cold). so if the total weight is 190g and its length is say 400mm, the top of which has a M8 brass bolt soldered to a small angle plate for an offset, the bolt is in the hull and the tube has to match the centre of the keel, and the base of the tube is a small piece of brass plate drilled and slid onto to the bottom and then soldered facing forward by up to 40mm - acting like a tray for the balance weight which is either a single or double 53g galvanised washer, I think it was 2 so that makes up 106g at 400mm from the keel, not an issue for a large sailing vessel with a 1m mast, but this is a small 300mm+ vessel, not wishing to give weed a chance to wrap around a fin and bulb.
 
An original thought was to have a brass plate cut diagonally across the corners creating a triangular plate x 2, then using a dremel, cut a slot down the centre of the tube, wide enough to accept the edge of the brass traingular plate (almost like a rudder), then top it with a brass bolt (this screws into the hull through a special hole), then bolt the weights on to each side of the traingular plate like a sandwich and profile the bottom point to be flush with the washers, then cover in thin plastic card or just paint.
 
problem with this is the weight calculations, the overall length would be shorter than the 400mm, some of the weight would transfer up to the hull thereby reducing the pendulum effect, meaning that more weight would be needed to give the righting motion of the weight and hense the hull would end up lower in the water, detracting from an asthetic point of view.
 
Alternatively for strength place the traingular plates side by side a solder together, then fix the bolt and the weights as above, still I would have the same problem with weight.
 
Ideally I would prefer to remove the galvanised washers fitted inside, as ballast, and transfer these to the fin as a bulb, but will have to see how that turns out - now wheres my web cam, as a way of seeing whats where. 
 
adendum:-
the attached is the pendulum fixing point, the white strips left and right are plastic card, that was pre installed before the halves put together, this allowed a substantial amount of glue to be applied and acts as a positioning strip as well, it extended well to the rear and forward above the expected waterline, it allows the screwing of an M8 bolt into the underside, though I did find a M6 version and should have used that - and will on the future ships, the issue is that at least 2 x 53g galvanised washers are in the bows area - left of the picture is the bows. there is a place in the hull that would now be in the right of the picture (when the servo came loose) where I can cut it out again and attempt to remove the washers - though fixing it again will be a spherical ache.

[warspite]

the sketch to the left is the current pendulum, the sketch to the right is what is prefered though as the brass plate is already cut it does limit what can be done. Is there any calculation or material choice recomended for the creation of a light fin and heavy bulb?, I suppose if it is not a fast boat then the strength of the fin is not as important as it is not under a lot of strain. I could mod the plate to remove the tube entirely then.

[JayDee]

 Hello,

The usual way of making a Keel which will not collect weeds is as per my drawing,
I have done better drawings!!!.
Any Ballast needed should be placed at the bottom of the keel for maximum stability.

John. 

[warspite]

Yes Ive seen this type, again it is the materials and a way of keeping the most weight at the lower level to maintain a righting moment, a thin and light fin in any shape with all the majority of the weight at the bottom, in the sketch the 40mm square x 6mm thk blocks are the washers, if I can just remove those from inside it would be easier to add them to the bulb area without losing trim (I dont really want this vessel sailing on its side, as due to the construction method, I built here in one half and attached the other when closing up, so the closing up side is an unknown as to being fully sealed).
 
If the brass sheet is just thick enough, I could dispence with the tube portion, I could move the ballast so that it was angled and therfore at the tip  and may still give some equal trim for and aft of the bolt.

[JayDee]

Hello,
Using brass sheet you will have a lot of the keel weight too high up.
Keep the brass tube and ballast,but use plastic sheet in a shape similar to my drawing to blend the keel into the hull.
At the moment you have designed a very good weed catcher!.
John.
 

[warspite]

Bow of the boat is to the right and the bulb is trailing so the angled section is slicing through the weed. 
 
In the next few weeks I am off work so will have a go at getting in and trying to remove the weight, though now i am thinking about it I want to do it now - its just toooooo coooolld, bruurrr.
 
Just as a thought, I have seen pictures where there are sails between the main mast and formast, was this a common practice and did they help in any way (though in the films they never show this).

[JayDee]

Hello,
Your boat is not heavy enough to "slice through" any weeds.
All you can hope for is to deflect them.
I suggest you buy a pair of waders.
John.
 

[warspite]

Darn it - thought of creating a sharp knife edge with the brass leading edge, might get told off for going equiped,lol

[tobyker]

Sails between the masts - look up staysails, and "fishermen's staysails". I suspect they are more use at 1:1 scale where you have lots of blokes to run them up and down and trim them: not so easy to control them by r/c. But then if foresails work ahead of the foremast, staysails between the masts must work in the same way. So if you could control the foresails and the(square) mainsails, then linking the staysails to the foresail sheets might work. Hmmmm.

[warspite]

I just thought they gave push when the wind is from behind and just off one side slightly like directing the wind onto the next set of sails.
 
On a model of such a small scale I suppose they have no effect other than to push the vessel over if trying to tack.
 
Was just hoping they would help push forward rather than this boat going sideways, hense the idea to create a fin to help direct the push forwards.

[JayDee]

Hello,
Any chance of a photo of your boat ???
John.

[warspite]

I dont have any of the finished boat, only found that on my sons phone, he had deleted the rest.
 
that and its not completed fully.

[mrpenguin]

Just as a thought, I have seen pictures where there are sails between the main mast and formast, was this a common practice and did they help in any way (though in the films they never show this).

@Warspite:
I built a square rigger a while back that included a staysail. I usually sail with the staysail off as it does not do anything of value on an RC model without the capacity to trim it accurately. It just increases heeling from my experience.

Re the keel, I have not read all the talk on this, but the physics remain the same - it is pendulum keel and so it remains as a lever with a weight on the end of it - to reduce sailing depth while retaining the same righting moment you need the fin half as long with twice the weight on the end. The extra weigh drags the boat lower in the water of course leading to another set of issues. Use lead for the weight. If you can do a sheet fin as proposed would help a bit with weed issues, but the lower the weight, the better. 

See the link below for the square rigger I built, you may glean something from it.... It was built for a competition using recycled materials. A great fun build....learnt a lot...
http://www.youtube.com/watch?feature=player_detailpage&v=sTj-aqYUX9g

[warspite]

Quality, milk bottle floatation, maybe the school project would like to see that as a follow up for next year  , they could have their own sea battles with a way of taking a flag of the other boat.
 
So basically if I want to reduce the pendulum by half then I need to increase the weight by 2, theoretically, if I can get the other weights out of the boat and place them externally on the bottom of the brass fin then that will in theory help significantly, a bit of trail and error then 
 
Thanks for that. When building this boat I thought that plastic masts would break easily and a fear of them breaking meant that I made them in brass, there section would have been too thin to cope with the sails, but I may try an experiment to make the next boat with suitable lighter materials above deck.

[mrpenguin]

.... When building this boat I thought that plastic masts would break easily and a fear of them breaking meant that I made them in brass, there section would have been too thin to cope with the sails, but I may try an experiment to make the next boat with suitable lighter materials above deck.

From what I learnt building the recycle boat, with a square rigger there is little load on the masts, I could have made my masts smaller diameter and the spars a bit lighter but that was what I had available at the time. The many shrouds and sheets distribute the load to many parts of the boat so there are really very few high stress areas. With a square rigger there is sometimes load on the forward-running stays as well when sailing backwards (my square rigger sails backwards quite well). The mast load is really mainly vertical compression in any case. The only area on the boat under much tension is the bobstay, easily overloaded if one overdoes the tension on the many shrouds, they only need to be just firm, not tight I found.

As with any sailing model, adding weight / leverage below the water or reducing weight / height above the water leads to better outcomes. I had a free hand in the one that I built; if you are working to scale for a replica or such then you have some limitations to keep it looking right...

[warspite]

With this KIT, the masts are very thin moulded plastic  , thinnest about 2mm and some can be up to near 80mm long at about the top sail area, the mouldings are quite susceptable to warping, so structurally they were not that good, hense the brass, as the formast and main mast rotate via a solid link (borrowed from the aircraft side of modelling) and a servo, I was unsure if stock ABS tube would have been better, though not neccessarily lighter or would I be wrong on that score, would have certainly been less work with soldering etc, though the making of them was an experience never done before and sadistically enjoyable.
 
Some parts are better in brass as they allow a lot of give in handling and shore based obsticles - like concrete paving or walls cannot remove them easily.
 
I loved the rope linkages and the use of buttons etc, I tried to keep this boat quite simple, though a test sail did not give any confidence as it is underpowered for getting back to shore in a calm condition - tethered does not help. 

[mrpenguin]

With this KIT, the masts are very thin moulded plastic  , thinnest about 2mm and some can be up to near 80mm long at about the top sail area, the mouldings are quite susceptable to warping, so structurally they were not that good, hense the brass, as the formast and main mast rotate via a solid link (borrowed from the aircraft side of modelling) and a servo, I was unsure if stock ABS tube would have been better, though not neccessarily lighter or would I be wrong on that score, would have certainly been less work with soldering etc, though the making of them was an experience never done before and sadistically enjoyable.
 
Some parts are better in brass as they allow a lot of give in handling and shore based obsticles - like concrete paving or walls cannot remove them easily.
 
I loved the rope linkages and the use of buttons etc, I tried to keep this boat quite simple, though a test sail did not give any confidence as it is underpowered for getting back to shore in a calm condition - tethered does not help. 

@Warspite:

You have not mentioned the size of this boat - I am assuming about a metre long?

It sounds like the use of the brass for the masts was a good idea, even more so if you have rotating masts instead of sheeting the yards as I did. The rotating mast method has much less tangle of lines but the masts will be carrying more load. As you indicate, handling the boat can be a problem, they are easily damaged long before they reach the water...

Re the test sail - a square rigger is underpowered compared to modern sail plans, but generally has a lower centre of effort. The square rigger is totally different to sail to other sailboats (such as a Bermuda rig) - they will only point about 70 degrees to the wind at best (compare to Bermuda at around 20-30 degrees), so upwind sailing is a challenge. Downwind or reaching is easy of course. Tacking is generally done using a box turn (something like doing a three point turn with a car). The forward mast needs to be able to turn the sails separately to the after masts to allow steering and tacking.

This video shows most of the sailing manoeuvres for a square rigger as well as more on the build. See 8:50 through to 9:20 for a quick look at most of the moves:
http://www.youtube.com/watch?feature=player_detailpage&v=zZGjFR5CYUE

[warspite]

Yeeeaaaa, about that, the boat is an off the shelf conversion  , it has rotating for and main masts, both rotate at the same time in the same direction, the rear mizzen is fixed but for the triangular stay type of sail over the stern, which is free running, well slightly tethered, thought was that if the rudder turns the vessel right, the triangle sail will push over to the left assisting the turn (in practice it has no effect at all - maybe size is the problem  ). The vessel is about 450mm overall in length - including the bowsprit - he said sheepishly, surprisingly the vessel could take a lot of weight when it was just the hull put together and sat in a body of water, it took about 500g+, though this never works out as you expect, as the majority of the weight ends up above water - darn it.
 
With the counterbalance as drawn, it sits quite straight and level, even heeling it over, it returns quite easily to vertical, its getting the same effect with a smaller fin and bulb that I am more interested in, I'll have a look at the vid in a mo.   

[warspite]

Fantastic, reverse gear as well, I know they are difficult to control and though this was an experiment, I quite like it and want to build its sister and then go on to some competition, its getting the balance right, I could have just made it run on props but that would be cheating. I dont have access to a body of water with nice clean accessible edges and no weed, and wildlife, or a rescue vessel, most of my boats are plastic fantastic WWII vessels, 1 is too small, one is a 1/72 MTB vosper and nose dives, another is long and slim and takes an age to get any where and the corvette hasnt seen water for near on 6 years if not longer. 
 
work you have to do it. 

[mrpenguin]

@Warsprite:

Yes, at 450mm long including the bowsprit it will be extremely difficult to sail I would think. If you are considering building another, I suggest you plan  something around 900-1000mm long (overall) - any bigger and transport becomes an issue without de-rigging.

I found the aft sail (it is a spanker on my recycle boat) was not much help. I also found the flying jibs had a marked effect on direction control being so far forward of the centre of the boat, only small sail area but a lot of effect. With mine, the forward mast is more useful in controlling direction than the rudder at times,  even with increased rudder size. The main and mizzen mast sails all swing together and work as a team. The differential between them and the foremast provides most of the control and manoeuvrability.

[warspite]

So Ive been reading it wrong when I read threads on how to operate the masts  , on several they operate the for and main, which is what I have done, I pressume the rear two operating sets up different aspects to a tail or side ways wind, my rear mizzen is fixed and is why it may not operate as well, it might be something I can change on others if the space is available and a little bit of 'adjustment' on this one using a little inginuity.

[JayDee]

Hello,
We seem to have got away from sorting out the Keel position, onto other things!.
All yachts with sails need a Keel, but, where to put the keel to enable the boat to sail correctly?.
Too far forward on the hull and the boat turns into the wind, to far aft and the opposite happens.
Things here are getting rather complicated, so I suggest a visit to the following website.
http://www.onemetre.net/
This site is one of the best I know about, not an easy site, but very good.
Follow the advice given and you will only make ONE Keel !!!.
I have two very large boats built with the same info. 
Both boats are a pleasure to watch and to sail.
John.  

[warspite]

Thanks for the link, in retrospect, I need to make the fin as light as possible, maybe thick plastic card attached to a brass bracket attached to the screw, and then put the washers or lead weight at the very bottom edge, if I can get the washers out of the hull, will see what weekend brings, I am pressuming the fin will give some control on side ways drift, being that it is similar to a rudder.
 
As for the sails, that question was just to enquire if the installation of a stay sail ? could give more control like the rudder, but obviously not.
 
Until it is run in anger I wont know the answers, just would prefer to have a shallower keel fin before hand as the current set up will act like a trawler.