Tammie Norrie Transom shape with 6mm plywood

[VT_Jeff]

I've been studying my plans and one thing that's become clear is that using 6mm plywood will present a few challenges. The jogs on the transom are drawn for 9mm plywood. There is a note at the Hog to leave it 3mm wider on each side for 6mm plywood, but translating the jogs is down to me.

I THINK what I need to do is just come OUT at each jog 3mm, so if you measured across the transom form jog to jog it will be 6mm wider total than if I were using 9mm plywood, meaning the ultimate transom/planks shape will be roughly the same widths as it would be if I were using 9mm. This may seem obvious, but the other option would be to shave the outside of each jog down 3mm, so the transom/planks would end up 6mm narrower. This has merit because the boat will be narrowower at each station.

This is my first lapstrake so I'm sure I'm mutilating the language and possibly being quite dense, I'm sure it will all be clear once it's not important anymore. Any thoughts appreciated.

Jeff

[willin woodworks]

Why not just use 9mm ply?

[wizbang 13]

This is an epoxy boat right?
Why sweat 3 mm ?
Thats a coupl o pumps .
Or...stick with the plans .

[VT_Jeff]

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[VT_Jeff]

This is an epoxy boat right?

Yes

Why sweat 3 mm ? That's a coupl o pumps .

Figuring out what I do and don't need to sweat is at least half the battle here but you make an excellent point: I could cut it to plan and fill the gap with peanut butter. Not sure if this is my best-bet but definitely an option to consider. It also helps in visulaizing how I do need to modify the transom, so thanks.

[VT_Jeff]

Why not just use 9mm ply?

Fair question. I already own the 6mm, and am committed to it anyway for weight savings. And I'm a stubborn SOB, an important quality for any boat-builder I think.

[VT_Jeff]

Or...stick with the plans .

The plans call for either 9mm or 6mm, they just tend to show more detail for 9mm, such as with the transom jogs.

[wizbang 13]

I'm all for keepin em light.
I feel most amateur built boats , and boats designed for amateur builds , are far overbuilt.
The things (structural gaps) I have done with epoxy would shock most,but never a failure.

[VT_Jeff]

The things (structural gaps) I have done with epoxy would shock most,but never a failure.

I went with the lightweight version on my previous 2 boats, both SnG. I'm glad I did on both, no regrets so far.

[jpatrick]

Cut the jogs just deep enough to accommodate the thinner ply. Then the outside dimensions of the boat will be maintained. Just about every boat design's table of offsets gives dimensions to outside of planking for a reason.... It is those dimensions that define the boat's form.

Jeff

[VT_Jeff]

Cut the jogs just deep enough to accommodate the thinner ply. Then the outside dimensions of the boat will be maintained. Just about every boat design's table of offsets gives dimensions to outside of planking for a reason.... It is those dimensions that define the boat's form.

Jeff

Thanks Jeff.

Prompted by your comment, I just looked at the plans and this is apparently the exception: "Offsets are in inches and sixteenths to the inside of planking and forward face of transom". I wonder if that is to accomodate the choice of planking.

I think that solves the riddle of which direction to adjust.

[Bill Wiegmann]

Perhaps this is worth emailing Iain about (iain.oughtred@gmail.com). I built my Tammie Norrie hull from a Hewes & Co. kit, so I do not have any direct experience here, but Iain's mold patterns show the 6mm garboard as contiguous with the outer face of the 9mm garboard in order, I believe, that the keel dimensions would be the same in either case. (If the 6mm garboards lined up with the inner face of the 9mm, the keel would have to be narrower than drawn.) For the other planks, however, I would have thought the curved lines on the mold patterns themselves should be followed (effectively tracking the drawn dimensions to the inside of the planking). You might try actually drawing 6mm planks on the mold patterns to verify before cutting out your transom.

[VT_Jeff]

Perhaps this is worth emailing Iain about (iain.oughtred@gmail.com). I built my Tammie Norrie hull from a Hewes & Co. kit, so I do not have any direct experience here, but Iain's mold patterns show the 6mm garboard as contiguous with the outer face of the 9mm garboard in order, I believe, that the keel dimensions would be the same in either case. (If the 6mm garboards lined up with the inner face of the 9mm, the keel would have to be narrower than drawn.) For the other planks, however, I would have thought the curved lines on the mold patterns themselves should be followed (effectively tracking the drawn dimensions to the inside of the planking). You might try actually drawing 6mm planks on the mold patterns to verify before cutting out your transom.

I dropped him a note to see if he wants to weigh in, thanks for the email.

You're exactly right about the positions at the keel. It's just a matter of where to go from there: follow the inside face shown or the outside face shown, or some of each depending on if I'm on the inside of the curve or the outside.

Drawing in the planks is my plan as well, I suspect the mystery will reveal itself once I do.

[KenStocker]

Like Bill, I bought the kit, with the transom pre-cut. So I'm not much help either. But I love watching someone else start the TN, and will be following along. There might be at least one or two questions along the way that I can at least tell you what not to do! Ha!

Ken

[VT_Jeff]

Iain did get back to me and offered some ideas, and acknowledged that there may be some room for interpretation there.

"Interesting question; i have thought it might be slightly confusing, where the garboard twists into that reverse curve. And the bevel for the next plank shifts the next strake instead. The idea was that you cut that wee notch in the transom, so the garboard sits at the lower edge of the plank land. Looking again, i wonder if it could be set into the transom another 2 or 3mm, so we get a wee bit closer to the original lines plan curve. It may depend on how far the garboard can comfortably be twisted. The 6mm plywood may be ok; 9mm not. We just don’t want to cut more of a notch in the transom than we can fit into. "

So, with that, at least I know that the primary drivers are 1. sticking to the original curve and 2. not trying to over twist the garboard and 3. notching minimally. Maybe not in that order.

I'll make a few tracings of the transom plan and start drawing in some 6mm-based nothes and see what I can come up with for a reasonable compromise between those possibly competing criteria.

It's going to be some time before I actually put saw to wood on the transom so plenty more time to mull it over.

[VT_Jeff]

Been a while, got caught up doing some upgrades to my other 2 built boats but I'm back at it, full steam, at least for another month.

Another newbie question: The materials list on my plans shows, for example, that the stem requires lumber @ 1-3/8" X 4", 4'. Measuring the plans, the stem shows to be, for example, 1-1/2" thickness at one point and 1-5/8" thickness at another. 1-3/8" clearly isn't going to work. Lumber is generally bought in quarters, 4/4, 5/4, 6/4 etc, so I'm confused where 1-3/8" would have come from: it's not a commonly sold thickness for hardwood, and also won't fit for the needed piece. I know how to make the piece I need, I just want to rationalize the 2 pieces of mis-matched data, if possible.

Thanks,

Jeff

[Edward Pearson]

I have a few things to say.

1. Don't forget there is also a bevel where the gunwale upsheer meets the transom top edge under the transom ears.

2. TN also have utiility used with a little outboard now and again, when the need arises so a fairly stout transom is good forward thinking for any of that.

3. You'll either need to choose a fillet on the inside, a transom frame or solid planked transom. For a varnished boat, even a colour matched fillet looks a little unsightly (my old TN) a frame looks nice but is a fait bit of work done properly (my Shearwater) while planked up is prone to opening up with sun on it and timber movement (a Gannet we had). Having had and done a few of these in all different styles, I think the best way of having all advantages is a planked up transom with glued in splines and on the outer face, your plywood then you've got a stout transom for the outboard and transom fittings, wide lands for the planks so you don't need fillets, and don't need to make a transom frame.

After cogitating it for months from the moaning chair, you'll final fit the planks by standing aft and eyeballing them with a Shinto rasp and going at it bit by bit. If this a painted boat, and there are good reasons it should be, then there's alot less fussing to be had and I'd reccomend you channel your 'Inner Bruce'.

[wizbang 13]

Geeze thanks Edward Pearson
finally getting a little traction here
Bruce

[Edward Pearson]

Been a while, got caught up doing some upgrades to my other 2 built boats but I'm back at it, full steam, at least for another month.

Another newbie question: The materials list on my plans shows, for example, that the stem requires lumber @ 1-3/8" X 4", 4'. Measuring the plans, the stem shows to be, for example, 1-1/2" thickness at one point and 1-5/8" thickness at another. 1-3/8" clearly isn't going to work. Lumber is generally bought in quarters, 4/4, 5/4, 6/4 etc, so I'm confused where 1-3/8" would have come from: it's not a commonly sold thickness for hardwood, and also won't fit for the needed piece. I know how to make the piece I need, I just want to rationalize the 2 pieces of mis-matched data, if possible.

Thanks,

Jeff

Take final size information off Iain's 'Construction Drawing' sheet. What it says in numbers. Thats the size needed before you start shaping it with a plane.

You will buy your timber rough sawn - it's cheaper, so add a minimum 1/4- 1/2" thickness (or more) and plane down with a thicknesser/ planer/ plane of your chosen kind for a clean and vibrant surface to dimension. The materials list given might be 'nominal' sizes i.e before planed down. I just used a load of 2" and 3" rough sawn on my Shearwater. If you don't have bandsaw/ table saw etc then you'll have to buy closer to size and pay the extra.

The aft face of the inner stem will vary along it's course to the keelson because of the angle the planks make with it, requiring more or less to be removed from its sides. That's probably what you're seeing, measuring off other drawings. Or you're measuring width as seen with planking in place. Outer stem needs to cover the inner stem and plank ends and have its front planed down to the keelband width you can get hold of or choose to use. So that measurement is a bit custom to you.

People laminate their inner stems but it's not necessary and Iain doesn't show it this way: his drawings usually show a built up inner stem. It's less 'structural' and really just a piece of wood holding the plank ends together instead of an epoxy fillet. If you do laminate the inner stem, expect a little spring back. Then use this as a pattern for a sawn built up outer stem, so that fits to it with little trouble. I realised built up stems save time, spring, epoxy resin, clamps and sawdust only after I laminated one up...

[VT_Jeff]

I have a few things to say.

1. Don't forget there is also a bevel where the gunwale upsheer meets the transom top edge under the transom ears.

Thank you! I just started cutting the transom out last night and had seen your note so I left room for that bevel, not sure that would have occurred to me.

I have a few things to say.

2. TN also have utiility used with a little outboard now and again, when the need arises so a fairly stout transom is good forward thinking for any of that.

It's 7/8 cherry and feels VERY stout. Not sure if this transom will see an outboard or not but I'm pretty comfortable that the transom will not be the weak spot if it does.

I have a few things to say.
I think the best way of having all advantages is a planked up transom with glued in splines and on the outer face, your plywood then you've got a stout transom for the outboard and transom fittings, wide lands for the planks so you don't need fillets, and don't need to make a transom frame.

I really like the spline idea but it was not in the cards this time around. I did the glue-up with Gel-magic, same stuff I used extensively on my last boat/transom, time will tell how it holds up in the sun etc. Transom, keel, stem, sheerstrake and interior will be bright on this boat, the balance of the strakes will be some off-white.

Appreciate the thoughts and the input very much!

Jeff

[VT_Jeff]

Take final size information off Iain's 'Construction Drawing' sheet. What it says in numbers. Thats the size needed before you start shaping it with a plane.

This is what appears to be inaccurate. It says 1-3/8 thickness on the Construction Drawing, the width varies from the forward vertical to station 1.

20230123_100034.jpg

You will buy your timber rough sawn - it's cheaper, so add a minimum 1/4- 1/2" thickness (or more) and plane down with a thicknesser/ planer/ plane of your chosen kind for a clean and vibrant surface to dimension. The materials list given might be 'nominal' sizes i.e before planed down. I just used a load of 2" and 3" rough sawn on my Shearwater. If you don't have bandsaw/ table saw etc then you'll have to buy closer to size and pay the extra.

For the transom, I got some 10" 4/4 cherry at Greenfield Forest products, ripped it to 5" for jointer, planed it in the thickness planer, glued it up and hand-planed the joints/squeeze out to a final thickness of right around 7/8". Glad I did not go 5/4, would have drown in the chips! Ripping down to narrow pieces and re-gluing is, I find, a good way to limit loss from cupping.

People laminate their inner stems but it's not necessary and Iain doesn't show it this way: his drawings usually show a built up inner stem. It's less 'structural' and really just a piece of wood holding the plank ends together instead of an epoxy fillet. If you do laminate the inner stem, expect a little spring back. Then use this as a pattern for a sawn built up outer stem, so that fits to it with little trouble. I realized built up stems save time, spring, epoxy resin, clamps and sawdust only after I laminated one up...

I had originally considered laminating but some notes from Ian and posts like yours have convinced me otherwise.

Really appreciate the input, great confidence booster knowing there are folks who have been down the road before and are willing the share their experience!

Here's my progress thus far. Band-sawing this transom is providing a "fun" challenge!

20230122_191429.jpg

[Edward Pearson]

I don't have TN plans to look at.

Are we talking inner stem or outer stem Jeff?

The aft surface of the outer stem is 1.5 inches in all three pictures. That's to cover the forward remaining surface of the inner stem after you've bevelled it appropriately and to cover the angled plank ends. With ballpark 1/4" ply a bit at an angle, that's just under 1 inch of timber wide at the forward face of the inner stem then or 14/16th's by your rule.

The aft surface of the inner stem is wider due to the angle in of the planks coming in what the measurement there? It will be full width, square edges aft at the sheer where its bluffest, and further down where its more acute, th width will be narrower between the planking.

Rule of thum I have, never cut anything off or make it smaller untill you have to!

I'm sure your Cherry transom will be fine and look tremendous. Other things like just parking it so the transom doesn't face the mid day sun or having a cover with a transom flap will keep the sun off it will help prevent any movement. If you're varnishing it, a cover that goes down the side and covers the topsides and transom reduces weathering and bleaching hugely too.

You've used sheet material for the molds, if you have the offcut parts still, you can use them for bilge support when you turn it over and to set your trailer rollers/ bunks up etc before the boat goes on.

One other thing... it's easier to mark center and perpendiculars now to cut clean perfect holes in your transom for the rudder gear especially with that drill press you have in the back ground rather than eyeballing it later with a hand drill. I'd say an ellipse is worth the bother over a rectangle for the tiller hole if you can.

The Tammie Norrie has a hollow waterline entry, as many boats do Jeff to reduce entry angle fro slow speed efficiency. That means around about station 1 at the waterline, when you bend a plank around you might need to anchor it in the hollow rather than allow it to sit convex around the hull as most bits of wood will prefer to. It might sit here naturally, it might not. Just saying watch that bit if you aren't mechanically fixing the planks to the molds. I used Oughtred's clamps and they worked mostly, but sometimes thought I might have been better to screw them down. I wanted a varnished boat though...

[VT_Jeff]

Are we talking inner stem or outer stem Jeff?

Outer, Ed. He refers to the Inner Stem as the "Apron". Your comments confirm what I suspected, that the 1-3/8 is off by an 1/8, I just can't see any other explanation. Not any kind of an issue, just serves to remind me that I need to cross-check.

I'm sure your Cherry transom will be fine and look tremendous. Other things like just parking it so the transom doesn't face the mid day sun or having a cover with a transom flap will keep the sun off it will help prevent any movement. If you're varnishing it, a cover that goes down the side and covers the topsides and transom reduces weathering and bleaching hugely too.

Thank you, Agreed! Solid idea on the transom flap! My other builds have some amount of brightwork on each and keeping it covered is something I'm trying to be better about.

You've used sheet material for the molds, if you have the offcut parts still, you can use them for bilge support when you turn it over and to set your trailer rollers/ bunks up etc before the boat goes on.

That's a great idea. You may be a wood-stove-firing or two late on this suggestion, unfortunately. Got me thinking though!

One other thing... it's easier to mark center and perpendiculars now to cut clean perfect holes in your transom for the rudder gear especially with that drill press you have in the back ground rather than eyeballing it later with a hand drill. I'd say an ellipse is worth the bother over a rectangle for the tiller hole if you can.

Gotcha, I'll study up on that piece and plan on those mods while the transom is still loose.

The Tammie Norrie has a hollow waterline entry, as many boats do Jeff to reduce entry angle fro slow speed efficiency. That means around about station 1 at the waterline, when you bend a plank around you might need to anchor it in the hollow rather than allow it to sit convex around the hull as most bits of wood will prefer to. It might sit here naturally, it might not. Just saying watch that bit if you aren't mechanically fixing the planks to the molds. I used Oughtred's clamps and they worked mostly, but sometimes thought I might have been better to screw them down. I wanted a varnished boat though...

Understood. Was not planning on fastening to the molds for the most part but since all but my sheerstrake will be painted, I have plenty of options. Appreciate the heads-up on the hollow, that point had definitely not matriculated itself into my melon.

[VT_Jeff]

The fog continues to lift, slowly.

Doing this in 6mm means that all of my forms should have been cut oversize by 3mm to maintain the outside dimensions, as someone alluded to earlier, which went right over my head. I did not do this. I don't think it's an issue, I can just pad the landing areas by 3mm, which is probably simpler than trying to oversize the entire shape.

I was scratching my head about the inner stem(Apron) thickness as well as the outer stem: the plan calls out "sided 1-5/8" for the apron but measuring the plans, there are definitely areas where it's drawn thicker. I think I now understand that it's not critical to hit that max drawn thickness, it just means that there will be a small step where the garboards meet the apron, which I don't believe will be an issue. The outer-stem thickness is more critical because it needs to cover the ends of the planks as Ed pointed out. I'm in this to learn, primarily, so all is good; I'm learning!

I picked up a batch of Doug Fir today in Williamstown to start making the Apron and Keelson. Chips should start flying tonight hopefully.