6th Jan 2012, 03:26 PM #1
Adding bouyancy - retrofit tanks or simpler solution
I have so many questions as this is my first boat, I should start a 'general calls for help' thread, but maybe starting seperate threads each time will be best. (I'm considering a thread name change already)
I have a 12'6" catspaw dinghy, bought a few weeks ago, again, my first boat.
Strip planked in spruce, epoxy glued and sheathed, single layer matt weave inside, 2 layers of bi-weave cloth on outside. Mahoganhy makes up most of the 'non hull' timber. (made from the wooden boat magazine book/plan in the late 80's)
Inside is varnished, outside painted.
The seat layout is not real functional for my single person sailing (the majority of its use) - I sit in the hull between the stern seat and the rear thwart (fitted to the rear of the centreboard casing). Its a V-hull, with a 60 square foot sprit sail (11'6" for both mast and sprit), and in 10 - 15 knot winds I have not needed to hike at all, 15 -20 knot I just had to lean back hard on the hull (I'm @ 120kg's in weight).
I want to put in bouyancy. (I have been using old car inner tubes lashed under the seats)
What are my options?
Please bear in mind that a part of the enjoyment I get from this boat is from the look of its sexy interior, e.g. if it were fiberglass/plastic, I'd see it as 'just a tool', but I really like the look of timber.
I have large H. Mahogany boards, and maybe 2 (+) cubic meters of spruce/pine/fir boards (fast grown, light, rubbishy stuff, but mostly 1/4 sawn), I can work timber pretty well and also have no dramas laying 'sexy' veneer over ply, and can do 'fair' job of epoxy encapsulation (ok, a crap job for pro's, fair for weekend warriors).
The way I figure it, the options are:
1. get some thick pvc bouyancy bags made up for stern seat and under thwarts.
2. make a ply bouyancy 'tank' to fill the space between the front thwart and mast partner but instead of fixing it to the hull, put a bouyancy bag in it, and a bouyancy bag under the stern seat.
3. combine option 2 with extending the stern seat so that a bench runs along the hull to the rear thwart.
Future mods will be:
I know that in the future I will replace the sail with something bigger and able to be reefed (maybe a lugsail will suit),
The pivoting centreboard is giving me annoyance... its jamming as its too tight and is not so much a foil as a rounded board... the casing is capped off, and I may want to take the top 'capping' off and replace the cb with a foil shape. I raise this as the bouyancy mod should not have to be redone if I change other things.
As always, apologies for a long post and your thoughts and assistance will be gratefully received by this 'all things boat ignoramous'.
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6th Jan 2012, 04:58 PM #2
You have a wooden hull. Buoyant.
You have wooden centre board, rudder, oars.. Buoyant.
I assume your mast is also wooden. Buoyant.
Your boat is not going to sink, until the epoxy breaks down and starts letting water soak in to your timber. That might take a few years.
If you are worried about being swamped, get some one to teach you to sail up from that position. Always carry a good bailer.
Paul.I FISH THEREFORE I AM.
6th Jan 2012, 05:45 PM #3
If you were going to add buoyancy, portable buoyancy bags that can be lashed under the bow and stern thwarts/seating are the way to go IMO, for looks, portability, ease of use and ongoing maintenance. Ideally, I see a canvas/woven rope bag with an internal PVC bladder that can be inflated and tied with rope straps under the bench seats/bow thwart.
This'll compliment the traditional look of the boat, without altering its present construction at all. If you want to modify the boat later for ease-of-use, then factor the possibility of an underseat floatation in there, but this is easier. I've used this system on a Heron for many moons, and found it preferable to the inbuilt tanks it also has in pretty much every way.
6th Jan 2012, 06:13 PM #4
How about a couple of self bailers, fitted in the boat.
As long as you can get the boat moving, they will help you get rid of the water in the boat.
Also good for keeping the boat dry on land, if it is not under cover.
PaulI FISH THEREFORE I AM.
6th Jan 2012, 07:01 PM #5
The obvious question is why do you think you need buoyancy?
The obvious places to install some buoyancy is as chambers; one aft under the seat and one forward under the thwart at the forward end of the case. These could be done simply and lightly from 1/4" (6 mm) plywood (natural finished if you like). These boxes would be screwed to the underside of the seats and thwart, sealed tight with internal fillets and lastly fitted with a deck plate so they can be opened for storage and ventilation.
All these floatation chambers will do is permit a swamped boat to float higher in the water, which may be enough to let you sail off and if installed with appropriate scuppers, and self drain. Without the buoyancy chambers (boxes), the boat will swamp, but you can pretty easily bail it out enough to get back in an either continue bailing or sail off and let the scuppers do it for you. Of course you could always install a pump, which should bail out your boat as quickly as it's rated for or if manual, as fast as you can muster.
I'll guess that you have a minimum of sailing experience and feel you need the extra "security" of buoyancy chambers of some sort. You really don't. The Cat's Paw is a well known and loved boat, world wide and she sails just like she looks, easy and graceful. You can capsize her, like any small sailboat, but she'll have been warning you for some time previous, when this event occurs, so it's not really her fault it she does auger in. In the event of a capsize, she's easy to right, though she'll be half full off water. You simply turn on the pump or start stroking a manual or get out the plastic milk jug with the cut off top (my personal favorite) and start hand bailing. After a few minutes of wondering if the local sharks have noticed you're troubles yet, she'll be bailed enough to climb back in and continue on your merry, if soggy way.
This is a fact of life in open, unballasted little sailors. In fact, one of the best things you can do is intentionally capsize her, preferably in shallow and warm water. Then go over all the things you might want to do or discover what you need to do, in the safety of the near shore shallows. This way when you do manage to ignore all of her warnings and dump her over on her beam ends, you'll know what to do, how to right her, how to bail her, how to prevent the cooler full of beer from becoming an archeological artifact for some future explorer. Always save the beer, as it's a sin to the sailing gods to let it sink unretrieved. If you elect to leave it, they will haunt you continuously for the remainder of your sailing life, bringing ill winds and fickle currents always. I don't remember all of this wives tail, as I've never been foolish enough to off the sailing gods in this fashion, but I think it has something to do with suddenly becoming attractive to all the world's ugly women too.
6th Jan 2012, 09:27 PM #6you have a minimum of sailing experience and feel you need the extra "security" of buoyancy chambers
I also suffer from an excess of 'idiot confidence', and am often snapped back to reality in the middle of situations that I realise are edging into the sort of situation my ability can't handle... kind of the 'devil you know, but can't avoid because some part of your brain just wants to pick a fight with the bastard' sort of thing. e.g I know I will capsize in conditions I should have avoided, but decided that 'she'll be right and it'll be ok'... e.g I'm brave in the face of danger, but otherwise I like to wear a belt with braces.
I hear what everyone is saying:
It is bouyant enough on its own;
It has self drainers (yep, it does);
You can bail it yourself;
It is a boat that forgives fools.
I guess I should stick to the inner tubes, practice more the inshore capsizing (I have done this, but maybe I should do it more and think about the situation more)... but I worry about a swamping sea, with strong winds, swamping the boat as I bail.
To my mind, the less water to bail = less water to bail.
Maybe later I can make an informed decision to replace the inner tubes with the canvas bag idea that Asrainox put forward, or a pump as PAR suggests.
That seating layout is still a pain in the #### though... and that pivoting centreboard comes with its own problems of a centreboard that 'sticks' easily due to difficulty in cleaning (+ its not really a centreboard so much as a 'board')
As for beer getting lost... those future explorers will find the beer right next to my bones so no worries there.
I'll keep you informed.... thank you very much for your replies.
7th Jan 2012, 08:07 PM #7
My thoughts on the matter are quite different to PAR.
My only significant experience of capsizing sail boats was with Sabots & Wright
Intermediates as a teenager.
Both boats have smallish buoyancy boxes at the ends - about 7cu.ft of air total.
The Wright, especially, would have been unrecoverable after capsize without
them. The sort of wind which causes knock-down, also kicks up a chop.
Chop sometimes washed over the gunwales almost as fast as it could be hooshed out.
It was sometimes difficult to get it empty enough to sail on, even with
buoyancy boxes, auto-bailers, and a fit 15y/o energy with the bucket.
Without the buoyancy, it would not have sunk, but would have needed sailing
swamped to a nearby shore for emptying. This becomes a problem if the
nearby shore is either rocky, wharfs or a cliff. You won't die, but the boat
may cop a hiding.
With the exception of my slalom kayaks, stuffed full of polystyrene (and my
own designs) all the canoes I have owned have been woefully under-buoyancied,
making self-rescue afloat impossible.
My opinion is that's an uncool feature of a boat, especially in the middle of
SydHarb with its heavy traffic. I'm the sort of lazy maritime philistine who
prefers to self-rescue in situ, even if that comes at cost of appearance.
I'm therefore in favour of added buoyancy, however you choose to do it.
The canvas covered blocks lashed under forward, second & aft thwarts would
be perhaps most in keeping with the style of the boat.
As for the seating... hearing you loud & clear on this one. I'm going to have to
give up my Teal because it hurts me every time I go out for more than an hour.
Unlike Cats Paw, Teal isn't big enough to do anything about it.
You might try side seats between rear & centre thwarts. Make them wide
with a smaller leg-hole in the middle, rather like John Welsford's Rogue or Truant.
This will let you sit inboard or outboard according to wind strength. Fixed at
each end & a knee under the middle.
7th Jan 2012, 09:06 PM #8
Yep, Botany Bay has really fast and heavy chop when the wind is up.
And... In my lucid moments I know that my 'stuff it' moments will see me go out in conditions that are heavier than I can reasonably handle.
The way I see it... bouyancy can not hurt.
Add to this is the fact that the seating is a literal 'pain in the ####'.
The car inner tubes make righting it and getting going again easier... but look like... car inner tubes. The balance point for me is between the stern seat and the rear thwart, and I thought that (as shown by the photos) how the 'bench' could easily fit between stern seat and rear thwart using the exixting 'furniture' and a few 'hook and brace fittings' e.g. no screws required. I think that there could be at least 15 cube foot of bouyancy fitted in here. ? Surely that can't be a bad thing???
Dunno.... maybe I should capsize it and take a few pics and count the litres in it when I bucket out the water ... it seems to get pretty full to a clown like me.
7th Jan 2012, 10:44 PM #9
When I built "Miss Mouse" I had a bit of a dilemma over whether to fit buoyancy of not. I decided not to in the end as Mr Oughtred's design was so beautiful I did not want to spoil the look of her.
I have found the boat very stable and well behaved and I think it is OK with no buoyancy installed. I do realise that one day I might get caught out with a capsize, but I only sail her on an enclosed estuary. It is definitley not as exposed as I expect Botany Bay could be.
I love the traditional look of the open boat interior. If your Catspaw was mine, I think I would be having the same considerations but I don't think I would install in-built plywood tanks, it just wouldn't look right.
I would have a look at buoyancy bags though. I have seen these in a Tammie Norrie and they didn't look out of place. Bags used to be fairly common in dinghies back in the 70's. Don't know if they are still available in OZ, but Classic Marine in the UK have them listed. There is also a short reference article on their website about pros and cons. Welcome to Classic Marine
8th Jan 2012, 07:02 PM #10
Buoyancy bags are expensive and look a lot worse then a plywood box, particularly if the box is covered with cedar slats or something.
I've sailed the CatsPaw many times, though none recently and it's a light, very forgiving boat. It rises up, over boarding seas for the most part, not having enough momentum or heft to resit them. It's a fairly dry boat, considering it's size and what it is.
I've never like sailing a boat with thwarts, always preferring side seating, as I tend to hike naturally with puffs and shifts. A CatsPaw doesn't really have the room for side seating, so you're married to the thwarts and aft seat. It would be possible to make the wings on the aft seat longer, so you could move around to the side a little more, but it might spoil the look.
The best advice you could receive and take to heart at this point is: just go sailing in it, as it is. Sail in fair weather and close to shore. It's a protected waters boat, so you shouldn't be venturing very far past the swimming back to land distance anyway. Get a few dozen hours of fair weather sailing under your belt, then practice reefing, clawing off lee shores, heavier wind tactics, etc. Be prepared, by knowing how to reef long before you're force to learn the hard way. Do an inclining test, to see the point of no return, then continue this test into a full capsize and recovery. Pick a nice calm, warm water day and bring extra beer. You'll learn a lot about the abilities of this little boat and how easy it is, to get her back on her feet. You really want to learn this in a controlled situation, as a capsize is a sudden and often violent thing. You don't want to be in building winds, have a capsize, with seas breaking over you, as you attempt to learn how to right this little puppy, all the while trying not to panic or think about sharks.
8th Jan 2012, 10:25 PM #11
"the less water to bail = less water to bail."
spot on. tanks are also a great place to put those small things you wont need sailing but don't want to leave in the car or your pocket. dont put your bailer in the tank - dont laugh ive seen it way to often, usually by people that should know better. But if you do decide to fit tanks don't get carried away, a boat that bobs around like a cork can be just as bad. the board can be so high its hard to reach, and is (probably) more likely to go 180 rather than just have the mast lie on the surface, i like the board to be about chin high - easy enough to get onto but not so high that i need to climb in and over the top - but thats just personal preference. but whatever you decide the most important thing is to be able to self rescue. have a plan then practice it.
9th Jan 2012, 12:11 PM #12
Yep, I do try to go out every day, so long as there either some wind, or if its not glowing a gale. I make sure that I practice by setting a course that I have to stick to. Try stuff like sailing into the wind as much as possible, or doing circles around a bouy.
I've also signed up to do a season as crew on another larger sail/racing boat. Just a couple of hours a week... if other committements allow... and this should get my experience and confidence up. I'll just be self-moving ballast, so there should be time to check things out.
Another point is that the sail is as per the original design - I can't see that it can be reefed at all.
I'm hearing your comments about practicing sailing and recovering, and giving it time... however I guess the main point is that I'll need to do whatever makes sense to me and makes me feel more content. I've gotta be happy with where things are at.
Whatever I do will have to keep in with the appearance of the boat and not need stupid things done to the boat like screws through the hull.
Good point on too much bouyancy.
9th Jan 2012, 06:20 PM #13
Pic shows the concept.
Excuse the boards just plonked in.
8"/200mm wide seat is ok for my backside.
That will give me 31'/790mm between side seats at the rear. Between thwarts there will only be 13"/330mm between seat and centreboard case.
I'd probably remove the outer most sides of the stern seat, laminate up a colour & grain matched board to run from stern to forward thwart. Use the stern seat support and the thwart support for the majority of the attachment points, with a 'doodad' made from brass to give support around the rib stringers or a hidden webbing strap arrangement. Also add a 'support leg' that uses the floor stringers to support the centre of the bench.
Then put inner tubes in a canvas bag under that for the bouyancy.
This would resolve the bouyancy and seating issue.
Step one would be to give it 6 months or so of sailing, then mock it up in a ply torsion box.
Step 2 would be to make a decision and then do it in solid timber, using the torsion box as the template and former for bending the side seats to the curves needed.
Its council hard rubbish pickup in a few weeks, so if I see a dining table chair with a solid seat, I'll recycle that into a temporary side seat to see if that seating height works.
I feel better for having 1/2 a plan.
9th Jan 2012, 07:36 PM #14
The lower the seat height, the wider the seat top needs to be for comfort. The typical dimensions are 16"x16" (406x406 mm) for an average size person, but more often then not in a small boat, you just can't find 16" (406 mm) of rise to a seat. This is why seat tops are often quite wide. If you have a 12" (305 mm) seat top height, you'll need 20" (505) mm of width for your butt. Now these dimensions are just averages, but they're pretty close. As a rule, if you need to change one dimension, you have to add at least as much to the other, so (as an example) an 18" seat top would only need a 14" seat width, etc.
It's often best to make mockups of the available heights and widths, that you can get in the spaces you have, before committing to making saw dust. The CatsPaw needs to have a stiffener at the aft end of the daggerboard case. It doesn't have to be a full width thwart, but it does need to be a light beam, say a 1x2 (25x38 mm) set on the flat. This will keep the case where it belongs, without the bulk of the wide thwart in the way.
9th Jan 2012, 08:26 PM #15
Don't think I didn't hear your comments about the need for bouyancy... but this is my stress relief tool, and not having bouyancy (regardless of not needing it) adds stress to sailing it.
You should know that I'm now going to spend time sitting on different width and height boards now... bricks, board, backside, beer, television.
If the thwart doesn't need to be so wide, then should I assume that those laminated knees on top of the thwart don't need to be so big, or even there at all? They make 13" of the twart unusable as a seat.
I ask as the thwart knees can be removed by undoing 2 screws due to the way the original owner made them. e.g. only the mast partner knee is epoxied and riveted into place.
I 'could' replace the rear thwart knee and fair a curve from the mast partner knee, through forward thwart knee (replaced and made shorter) to a shorter rear knee, if I do the side seats, and if it looks good. I'd keep the rear thwart, as matching the curve of the stern seat sides, and curving the side seat up the rear thwart would make a wider place to put my backside.
Sounds like fairly major changes, but all this is able to be done without holeing the hull for fasteners, and able to be swapped out for the original fit, so it may be worth it.
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