Thread: The Little Black Dog - MSD Rowing Skiff - Adelaide OZ

Hi Richard, They didn't build it on a strongback - it was just being used as a work table.

I think a single screw - glue it in too! - at the frame heads will resolve the problem ... but woudl probably recommend the second screw as well.

You can get a feel for where the concavity is by laying a straight edge on the side of the hull. Instructive I guess, but not critical.

It will be OK and not give you any issues down the line.

MIK

Hi Richard
I hope the screw and glue works out.
There is a lot of arm wrestling to get things together with this boat and I am inclined to agree with you about building over a strongback. I would fillet and tape the chine inside and out though, quicker I think than turning that expensive timber into shavings. Another thing I would do is make the gunwhale from 2 pieces of 1/2" laminated on the boat with a 1/2" inwhale. Same thickness of timber for strength and a lot easier to bend onto the boat.
You mentioned concavity which reminded me that at one stage a couple of months ago when I was off work and looking at the boat everyday I spotted a concave section near the bow. I was horrified. I grabbed the straightedge to check and it wasnt concave, just less convex than each side. Since there was nothing I could do about it I forgot about it until I read that post, now cant even remember exactly where it was.
Its funny that when you are building something and looking at it and thinking about it all the time you see every little thing you have done wrong, every little or not so little stuff up you have fudged your way around and yet when you have finished no one else can see or even cares about it and you quickly forget the problems yourself.
And then you have your boat on the water, you have done something that most people dont even dream about and that is a real good feeling.
Tom

Howdy Tom,

Thanks for the feedback. I will have a strong positive response about the gunwale thickness ... just the thing that is useful to know. Does that fit in to your experience Richard?

Problem with a strongback is either you prefab the sides or you make a strongback. There is a big chance of a discrepancy if you combine the methods and whereever the difference is it means a lot of work figuring it out and fixing it with recutting the side or rebuilding the strongback.

Also I have had big discrepancy problems with trying to match the computer generated shapes with the strongback shape - it is less critical if the panels are not much twisted, but with twisted panels like the Eureka bilge panels the error was about 19mm

You could build with long legs on all the bulkheads to take them to the same level,

As far as bending the gunwale to shape goes, I didn't have any real problems because the horizontal curve isn't all that great and the vertical is barely there at all. However, I had huge problems with the amount of twist required of the stick and this is a problem right along the hull, not just where the sides go vertical at the bow.

I had to use clamps to hold it against the hull (this could have been done with screws) and clamps to pull the bottom of the stick onto the hull (this couldn't have been done with screws) - it was either that or leave a substantial gap to be filled with epoxy - by 'substantial', it felt like a comple of mm, I didn't actually get under there to look.

I could only do one side of the boat at a time because I used all my wooden clamps (the Sixpence clamps) to hold the gunwale in place and all my F clamps to pull the bottom against the hull - that same collection of wooden clamps did both sides of Sixpence at the same time so yes, getting the brute in place was an issue.

You should also note that I was using Radiata which is a stupid, cantankerous timber. A nice, fine grained timber might twist more easily.

The half inch laminations should be easier to twist into place but would introduce the complication of having to clean up the glue joint underneath (the top joint just disappears in the shaping process).

Would cleaning up that joint be easier with a square gunwale or a tapered one as per the plans now? We've essentially got that situation now with the double thickness area around the rowlocks but I haven't got under that to clean it up yet - any misalignment in the two laminates means you'll have to plane down the outer plank to match the inner. That shouldn't be a problem with a sharp block plane, even though it is on the boat - a square section could be done with a trimmer router.

Another potential issue with laminations is making sure you get the grains in the same direction - I wound up with the grain of the inwale running one way and the grain of the gunwale running the other so that when shaping the top of the gunwales, I was planing cross grain with one or the other - not much of a problem with a fine grained timber but radiata is horrid for this. I wound up doing the last stages of the shaping with the belt sander to get around this.

Richard

Originally Posted by Boatmik

Problem with a strongback is either you prefab the sides or you make a strongback. There is a big chance of a discrepancy if you combine the methods and whereever the difference is it means a lot of work figuring it out and fixing it with recutting the side or rebuilding the strongback.

Also I have had big discrepancy problems with trying to match the computer generated shapes with the strongback shape - it is less critical if the panels are not much twisted, but with twisted panels like the Eureka bilge panels the error was about 19mm

The twist in this boat's panels are the source of all the angst methinks, both in shape and the forces involved.

My sides had logs fitted top and bottom coz I'm an idiot and built the sides upside down to start with and maybe that affects this next comment, but maybe different sheets of plywood twist differently which can also affect the shape - I'm pretty confident they were cut to the plans and the plans were super accurate so this was easy to check.

Interestingly, on my boat, the hull has pulled away from the fixed side arms and both the temporary spreaders fell out during assembly - my hull wanted to be wider at the top than the plans. You could blame that log that was glued in place, but if it hadn't been there, would I have got a similar shape once I'd clamped on the gunwale as per the plans?

A straight edge along the hull where the side arms have pulled free (but clamped back in place) shows a concave of a mm or two - you don't see it without the straight edge.

You could build with long legs on all the bulkheads to take them to the same level,

I can't see any advantage unfortunately. It assumes a flat working surface (my shed floor is nothing like flat). I doesn't allow you to sit the boat at waist height unless you've got a big bench. Being able to shove the thing around is a blessing in a tight work space (which counts against the strongback argument). The legs won't sit flat anyway because the boat will pull itself out of shape. Rough as it sounds, unless the boat is locked down onto a fixed form, the best method is a set of saw horses, a tape measure and a spirit level.

Regardless of anything else, I'd remove the oversized legs currently in the plans. All they did for me was get in the way.

Richard

Thanks for that Richard.

One of the things is that while reducing the thickness of a section of a piece of timber just a little makes it easier to bend, reducing the thickness doesn't make it a lot easier to twist. But it will help!

Good point about the grain directions (god bless the belt sander)

MIK

I hadnt thought about the grain direction. That is a good point, especially as most of the best timber these days is only straightish grain. Can I add the power planer to the blessed list? St Makita?
Tom

Power plane? Dangerous rotten things. I've got my Dad's and everytime I use it it wreaks havoc, makes a mess and craps on the good rug. Sorry, I'm a darkside merchant (love me hand tools).

Richard

I nearly made this suggestion when the following comment was made in Tom's thread regarding the way his skiff blew around in the wind:

Originally Posted by Compass Project

I'd second MIK on reducing the skeg depth by an inch and trying her out. I played with Drake's keel and skeg a bit after launching, too. Often boats gripe to windward, that is the stern blows off...that indicates more skeg is needed, often times. But your bow blows off because it is a flat bottom and the stem is out of the water so there isn't much lateral resistance...so take the skeg down.

but I decided not to.

Then Mik made this comment in the disposable canoe thread:

Originally Posted by Boatmik

I am also thinking the bow fin might resolve a couple of things for the rowboat too.

Here's a photo of the underside of my Little Black Dog


This isn't strictly as per plans - the skeg is the same size but rather than sitting on a hardwood base, I have run a piece of 19mm sq. hardwood along the bottom of the skeg and towards the bow. It currently stops where the plans show it should.

Since this photo was taken, that 19mm sq hardwood has been rounded off - roughly a 5mm radius on each side.

Now for my suggestion - is it worth running the 19mm sq strip right to the bow?
It would answer Clint's suggestion that she needs more lateral resistance at the bow though he also refers to the bow being out of the water so some weight movement forward would still be needed.
It would be a similar solution to Mik's thoughts on a bow fin.
It's possibly less than either gent intended though Clint talked about a small reduction on the skeg to balance things so I don't think he was talking radical solutions.

I'm pretty sure I can make it so that it doesn't affect the looks of the boat (we're only talking 19mm sq).

Would there be any negative effects from doing this (apart from the extra work)?
Would it also help to reduce the 'pounding' that has been noted in choppy waters (even just a little)?
But most importantly, would it give the boat a little more directional stability in a cross wind?

Richard

It would help to protect the bottom when you drag it up the conctrete ramp.

Hey Richard!

Long time no visit! Thought I'd better pop in to tell you it looks as though you are going to beat me after all!

Cheers,

P

Originally Posted by bitingmidge

Hey Richard!

Long time no visit! Thought I'd better pop in to tell you it looks as though you are going to beat me after all!

Cheers,

P

Hey, the Europeans finally caught Midge and threw him out Welcome home mate.

Richard

Originally Posted by m2c1Iw

It would help to protect the bottom when you drag it up the conctrete ramp.

Not such a silly suggestion. I've heard tales of the metal strip on Gruff (GIS) and the lovely shriek it makes when dragged down the boat ramp

It would also look a little more complete to my eyes (though that's no reason to go adding stuff underneath).

Richard

It is not a shriek at all.

It is like someone is trying to grind a piece wood of wood down with a 50 ton concrete block.

But the hollow hull amplifies it 900 times.

It sound like serious damage is being done!

Or as Monty Python once put it

"This is the sound of an ant foraging for food amplified 5000 times ..."

"here is the sound of a horn beetle amplified 10,000 times (huge shriek) ... which scares the ant."