Thread: comments please on new boat design

Nice looking boats Arron

The problem with a continuous deck is that you end up sitting above the center of gravity. Swayback will help but then you end up sitting in a pool again.

Damned if you do, damned if you don't.

As for risers, If your deck is cambered then it's gonna be almost as strong as the hull. Mount your risers directly onto the deck. How much clearance do you need for the slides?

Alternatively, how about a coaming around the cockpit to reduce slop?

Just thinking out loud here

Rubber paints . . .

A narrow cat with the sliding seat between the hulls ?

Originally Posted by Darce

Nice looking boats Arron

The problem with a continuous deck is that you end up sitting above the center of gravity. Swayback will help but then you end up sitting in a pool again.

Damned if you do, damned if you don't.

As for risers, If your deck is cambered then it's gonna be almost as strong as the hull. Mount your risers directly onto the deck. How much clearance do you need for the slides?

Alternatively, how about a coaming around the cockpit to reduce slop?

Just thinking out loud here

thanks for the input Darce. Its appreciated.

There doesnt really need to be any clearance for the slides as such. They could be mounted directly on the deck, as is the case with most all-glass recreational rowing skiffs, some of which come very close to having continuous decks. The problem is that your heels need to be about 150-200mm below the top of the seat (thats from memory, not in a position to measure at present). This is to get your legs down and out of the way of the oars towards the end of the stroke. In the fibreglass versions thats achieved by moulding depressions into the deck, shallow long ones for your legs terminating in deep ones for your heels. I dont think I'd like to model that in plywood, though, very finnicky and probably inherantly brittle.

Actually, I'm not all that worried about the centre of gravity being a bit high. Stability is provided by the oars and very little is inherant in the hull.

When I proposed the idea of being sway-backed, I meant that the deck would still be cambered (upwards) all the way along - just significantly less in the middle. The main goal is to prevent there being anywhere that the water can pool.

There is already a coaming around the cockpit of the Oxford Shell. It does stop a fair bit of water coming in, but not nearly enough. Its about 50mm high and cant go much higher due to the rowing geometry.

All of this has come about because on several occassions I've found myself sitting in a pool of water thinking 'this doesnt really need to be here'. It should be possible to design the boat so water goes right over the top. Last time I got swamped, I rowed slowly into Patonga Beach, emptied it out, but then had to spend 15 minutes trying to get back out through the TINY shore break.

cheers
Arron

Originally Posted by Toymaker Len

A narrow cat with the sliding seat between the hulls ?

There are some very nice versions of that in the US. No doubt they are very easy to row and easy to relax in because of their stability. Though the cat is probably a better design all around, I do prefer the monohull though.

Maybe I'll build a cat later.

cheers
Arron

ps. Par. What does rubber paint refer to. Is that some way of sealing the gap around the risers ?

I think you may be underestimating how much stability you will lose with a higher seating position. I would suggest doing an experiment with the Oxford Shell by raising the seat to a similar height to your planned design and see if it can still be balanced.

Have you considered a bilge pump? The Rule500 is popular with sea kayakers and they also have an automatic version.
https://www.whitworths.com.au/main_i...AbsolutePage=1
https://www.whitworths.com.au/main_i...AbsolutePage=1

Originally Posted by KJL38

I think you may be underestimating how much stability you will lose with a higher seating position. I would suggest doing an experiment with the Oxford Shell by raising the seat to a similar height to your planned design and see if it can still be balanced.

Have you considered a bilge pump? The Rule500 is popular with sea kayakers and they also have an automatic version.
https://www.whitworths.com.au/main_i...AbsolutePage=1
https://www.whitworths.com.au/main_i...AbsolutePage=1

Hi KL and thanks for your input.

Stability is certainly something I will have to think about, especially as the intention is to make something which I can take into more open water. Thinking about it further, though, I'm not really sure that the height of the seat mechanism would be much greater when over an enclosed hull then it would be in the Oxford Shell (which is eminently stable). It isnt particularly close to the waterline in the Oxford for the reason I've mentioned - all to do with getting the legs down low, plus shortcomings in the way I made the seat arrangement. If I could draw better, I could work all this out.

That bilge pump is interesting. I had always thought that sea kayakers used manual pumps. What sort of battery do they use, and do you need to keep the electrics dry ? I'm just curious because it could have some use for it in my existing boats. For this exercise, though, I'm interested in building a boat that never lets the water in to begin with.

cheers
Arron

Now this is what I want to be able to do. Not deliberately, but I dont want it to be a calamity when it happens.

cheers
Arron

Of course you could build one of these. No problem then with sitting in a puddle or with stability.



the new ROCAT sliding rigger

Various batteries are used, I've tried sealed lead acid, a battery from a drill and multiple AA cells. All work with the lightest being a piece of poly pipe containing 10 AA cells fitted with end caps which would normally provide plenty of power for one day. I've bought waterproof switches from Dick Smith and if you cover the joints with heat shrink it keeps the water out. I would still recommend some sort of manual back up just in case.

G'day Arron
Is modifying the Oxford by raising your seating a few inches and
decking at or above water line with drains not an option ?
Something like these SOT kayaks
JEM Watercraft - Boat Building Accesories
Would probably need to keep a small foot-well below waterline, but
a dinghy auto-bailer would empty that quickly.
Could also add extra full height decking around the sides to reduce
the size of the hole for water to enter. Done in 2mm & 3mm ply,
it shouldn't attract more than a kg or so weight penalty.

Wouldn't turn it into a heavy water boat, but might be a quicker &
cheaper way to achieve your aim in the short term.

Or, since the North Bay is out of favour, take a jigsaw to it & perform
this same mod.
cheers
AJ

that rocat is very high-tech. Notice that its a sliding rigger arrangement, not a sliding seat arrangement. Apparently sliding riggers are more efficient and probably a bit easier to make as it doesnt have to put up with 90kg of lard crashing backwards and forwards. In this case it would allow you to bring the legs up equal to the bum because the knees are never in the way. I also like the way it doesnt require you to row crossover. I guess it has it all really, and would adapt quite well to being plonked on top of a monohull.

I wish this guy would turn his obvious passion for innovation to the problem of how to see behind you while rowing.

thanks for the info on the batteries KJL.

cheers
Arron

Originally Posted by b.o.a.t.

G'day Arron
Is modifying the Oxford by raising your seating a few inches and
decking at or above water line with drains not an option ?
Something like these SOT kayaks
JEM Watercraft - Boat Building Accesories
Would probably need to keep a small foot-well below waterline, but
a dinghy auto-bailer would empty that quickly.
Could also add extra full height decking around the sides to reduce
the size of the hole for water to enter. Done in 2mm & 3mm ply,
it shouldn't attract more than a kg or so weight penalty.

Wouldn't turn it into a heavy water boat, but might be a quicker &
cheaper way to achieve your aim in the short term.

Or, since the North Bay is out of favour, take a jigsaw to it & perform
this same mod.
cheers
AJ

Yep, two of my first thoughts exactly.

My first thought was why not just butcher the North Bay. I guess because its a nice piece of work and I dont want to butcher something which someone else might find useful, even if I'm not up to it. If I knew exactly what I wanted, it might be different, but I suspect this is something that might need a few versions. As its only 4 planks, it wouldnt be that hard to remake the hull - or very costly.

Then, when I saw this (picture below) I thought why not just extend the deck of the Oxford and put the slides on that - which I think is what you are saying. Technically it would work, but the same problem, I dont like butchering something I've done. Plus I would still like something lighter, slimmer and faster as I guess I"ve outgrown the Oxford a bit.

Ultimately, though, the real reason is that I like building boats, and its time to make another one.


cheers
Arron

Originally Posted by Arron

Ultimately, though, the real reason is that I like building boats, and its time to make another one.


cheers
Arron

Yep I understand a design of your own incorporating decks and why not a ultra light (nylon even) false floor under the slider to reduce the amount of water able to slosh around.

A thought re bailing, design a bilge pump system that uses the slider to power. You could get really tricky and use the winder mechanism off a battery less or dyno torch (generator in other words) to power an electric bilge pump. OK bit over the top perhaps.