Barrelbacked Overniter Build in UK

Designs for inboard or outboard power

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sproggy
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Barrelbacked Overniter Build in UK

Postby sproggy » Tue Apr 04, 2017 7:15 am

I reckon it's time to come clean about what I've been doing to plan my build. I'm currently recovering from shoulder surgery (seems unusually common on here?!) so unable to do heavy work in the garage but I've spent the time learning the basics of DelftShip, arguably completely ruining a perfectly good Overniter design and transferring the results first into an offsets table, then onto paper (full size) and at the moment onto 1/4" ply to make frame section templates.

Why? Well I bought Nimrod and Zip plans with the intention of building a Nimrod with a Zip-style upper half. But (a) I REALLY like a barrelback stern and (b) a "NimZip" just wouldn't work so well for the family. So I got back in touch with Gayle and ordered Overniter plans. The berths won't get slept in much (I may put in only one) but I will be able to put a porta potti under the foredeck which will likely be the favourite feature of the boat for certain family members..... So the Overniter offers the practicality I need but only half of the looks I want. So....deep breath....15" stretch, barrelback-style stern (the aesthetic effects of which will unfortunately be reduced somewhat by the presence of an outboard) and a single, continuous sheer. This results in changes above the chine to the transom and frames 1-3 - no major hydrostatic changes but a slight loss in bouyancy aft which'll be offset by (a) the extra length and (b) the fact that I won't be using a massive motor. I'll cold-mould the sides from mid-way between frames 4 and 3 back to the transom. The sides and the part of the bottom above the waterline will be strip-planked and finished bright and I'll paint below the waterline. These give an idea but there are some strange effects due to shading and I didn't pay much attention to the bow profile as I was concerned only with the details aft of frame 4:

Image

Image

Image

Some may ask why I don't just build a Barrelback. Well I don't have the space (I've already exceeded the length I can build in my garage but a cunning plan to add a temporary extra 3'6" does give me a bit of leeway if I completely ignore the fact that it won't fit once it's got a motor on the back and is sitting on a trailer....) and I don't have the budget to equip an inboard design from a mechanical point of view. And it has no 'accommodation'.

I hope to start transferring the frame template shapes to white oak within the next couple of months depending upon recovery time and family commitments. I'm fully aware that what I'm doing may not be to everyone's taste. Perhaps you think it'll look like a dog's dinner. Well that's OK - it's a very personal thing but I like the shape I've come up with, given my practical requirements and build space constraints. Others are free to have, and voice, different opinions. In the meantime I welcome comments and challenges about structural, constructional and other design implications of what I'm doing because, despite me qualifying to do this kind of thing over half a lifetime ago, there's a lot more knowledge and experience out there on the forum than in my head.

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Gayle Brantuk
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Re: Barrelbacked Overniter Build in UK

Postby Gayle Brantuk » Tue Apr 04, 2017 8:27 am

My technical comment is WOW. This looks like a very interesting project and you seem to know what you're doing, so let the fun begin! Thanks for sharing and I hope for a very speedy recovery...

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sproggy
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Re: Barrelbacked Overniter Build in UK

Postby sproggy » Tue Apr 04, 2017 8:40 am

Thanks Gayle :D I was particularly concerned about your reaction to such obvious messing with your father's design.... I think I know what I'm doing. I should know what I'm doing. But there remains a nagging concern that I may not know as much as I think I do! Perhaps this is healthy as it leads to me triple-checking everything I do - that has already saved me when I realised that my vertical transom measurements needed 2.2% adding (vertically) to account for the 12 degree slope. I'll get there, but it'll be slow.

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BayouBengal
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Re: Barrelbacked Overniter Build in UK

Postby BayouBengal » Tue Apr 04, 2017 11:35 am

Interesting. This is not too much different in concept than what I did with my boat, which is take a hull design that met various requirements that were necessary and then change the transom shape above the waterline to give the desired aesthetics.

But you my friend have a very distinct advantage over me in doing this in that you obviously have the ability to use a CAD program. I can't draw either with a program or without, so I had to shape the frames for the sides of my hull by trial and error while it was upside down on the building form, and then try to envision what it would look like when I turned it upright. Quite frankly, I was very concerned that it might look like what a dog produces after it has had dinner.

I think what you're wanting to do is quite doable and because you have the ability to draw it out in 3D and look at it ahead of time, I expect it will look a lot more like filet mignon than a dog's dinner.

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sproggy
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Re: Barrelbacked Overniter Build in UK

Postby sproggy » Tue Apr 04, 2017 1:13 pm

Thank you, but you over-estimate my abilities! For the record I will say what I did, which was kind of like using a super-computer to add up the cost of your weekly shop. I used DelftShip which is free to download - it's ship design software, not CAD software, but it does produce pleasing renderings. I taught myself the basics of it - little more than scratching the surface. I chose an existing hull design from the DelftShip online library - a hard chine planing hull. Actually a Riva, which caused a few problems of its own which I won't go into. I scaled it to match the length/beam of the Overniter. Then I imported measurements taken off the Overniter plans (heights and widths at sheer, chine, keel etc at each frame) and pulled the hull I'd imported into a shape that matched them. It's crude and not very sophisticated, but close enough. I then altered the lines to resemble what I wanted, twisting and turning the views to ensure that I got fair lines in all elevations. Once I was happy with the result (which took many, many hours, because I couldn't resist the urge to fiddle) I took coordinates off the computer model at the longitudinal positions of the transom and frames 1-3 and plotted them full size on the standard Overniter plans (the big sheet with the full size frames).

I then used ship curves and wooden battens to draw a fair line through the points I'd plotted for each of the 4 frames. This proved that the co-ordinates I'd taken weren't spot-on but that's OK - this is boatbuilding, not rocket science. So my fair curves were spot on at the chine and sheer (the two critical points) but didn't hit all of the interim points. It's more important that they're completely fair.

Having drawn the revised frame shapes I then had some fun with trigonometry in drawing the deck curves at the transom (which flows seamlessly into the side) and frame 1. Frames 2 and 3 won't have deck beams - just an 8" deck edge at the angle specified on the plans.

I would stress that my use of DelftShip was extremely crude - I used it simply as an aid to changing and envisaging the hull shape. Its capabilities are a world away from the early version of Autoyacht that I used as a student but I'm not good enough to take advantage of them.

I did think about taking your approach and modelling the changes by eye with plywood frame shapes mounted on a temporary form but with a duff shoulder, learning to use DelftShip was more practical than handling large sheets of ply! Having seen your build thread the trial and error method clearly worked for you. And then some. I can only hope my build comes close in quality to yours.

Ian

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NAMEngJS
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Re: Barrelbacked Overniter Build in UK

Postby NAMEngJS » Tue Apr 04, 2017 2:23 pm

I would first like to say that I really like the look of it. the finer or non vertical bow compared to the barrel back and the little deadrise that you have to the transom I would think make her ride smoothly in a rougher chop as the barrel back has no deadrise aft.

I have never used DelftShip before though I have heard of it. I typically use Rhino and MultiSURF for my modeling at work. I know both programs have curvature analysis features (like a Gaussian representation of the surface) and linear curvature analysis. If DelftShip uses C-Splines vs B-Spline Curves your lines may have minor inflection points that are harder to ensure fair. Another nifty way to help "See" the fairness is if DelftShip will export to any free cad software you can export the lines and scale the lines in one direction (For example If you have the "Profile View", your first rendering, take the sheer, chine and baseline and scale the vertical direction only) this will exaggerate the inflections of the lines in this direction and if there are flat spots or multiple inflection points you would be able to notice them if you can plot it on an Architectural "D" of "C" paper.

Yes you are building in wood so the benefit is that you can fair with sandpaper, plane, etc. but just for the sanity check it may help to ensure the lines are indeed fair enough to start. It may be the rendering but in both the profile and plan views there is a black line everywhere except from midships to about station 9, so i wonder if it is a) rendering issue or b) an inflection change (slight).
All men dream, but not equally. Those who dream by night in the recesses of their minds, wake to find that it was vanity: but the dreamers by day are dangerous men, for they may act on their dreams with open eyes, to make them possible.

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sproggy
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Re: Barrelbacked Overniter Build in UK

Postby sproggy » Wed Apr 05, 2017 1:16 am

Thanks for the pointers. Good idea about scaling up to improve accuracy and see any deviations from a fair curve. I am completely sure that my sheer, which is the most visible line on the whole boat, is fair in all planes as I can strip out all the modelling and see that line on its own. The chine is unchanged so that too is fair. What is in between those two fixed lines I have faired close enough on the computer and then refined the old fashioned way on paper at each frame, knowing that any longitudinal variations will be minor (+/- 2mm) and will be dealt with when I fair the assembled frames.

I alluded to issues as a result of using a Riva hull as a basis for my design in DelftShip which, in hindsight, was a mistake. This was a very complex design with compound curvature all over the place and a double chine which doesn't apply to the Overniter with its more simple construction. So I dumbed it down some but as you say there are issues with the rendering as a result of this. This was proven by the fact that even using unmodified Overniter offsets (before I made my changes) DelftShip still didn't consider that it was even close to being developable which it obviously should be. And yes, there's a funny effect at the sheer - an inflection that I worked around as I couldn't seem to lose it. So I consider the rendering to be an acceptable visualisation of the hull shape aft of frame 4 above the chine. It's irrelevant elsewhere - it gave me the basic information I needed to refine the result on paper. Not how a hull design application is intended to be used but I reckon I'm close enough. These are the lines I actually transferred to paper:

Image

The pink lines are those that relate to the Overniter, pink dots at frame locations. You can see that forward of frame 4 (where I'm not messing) the Overniter lines differ from the digital chine and sheer (black lines) but as long as I'm fair through from 3 towards 4 I don't mind as forward of there it's the original design. It looks as if the chine is off further aft too but that's the 'other chine' that I wasn't working to. It sounds as if you're a professional designer so you're probably shuddering at my approach but I reckon it'll work. Time will tell!

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NAMEngJS
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Re: Barrelbacked Overniter Build in UK

Postby NAMEngJS » Wed Apr 05, 2017 10:26 am

I am an engineer/architect and have done design work before and believe me we take our old designs and massage them to meet the particular customer's desire. Since you were able to check to see if it is develop-able then I think it is probably a non-issue. I know i will be tuning in to see how this projects turns out. :D
All men dream, but not equally. Those who dream by night in the recesses of their minds, wake to find that it was vanity: but the dreamers by day are dangerous men, for they may act on their dreams with open eyes, to make them possible.

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gap998
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Re: Barrelbacked Overniter Build in UK

Postby gap998 » Wed Apr 26, 2017 12:01 pm

Looks good Sproggy,

I don't know what files DelftShip can use but I have 3D files from my Super-Overniter thread if they are any use to you. I modeled using a trace of the Overniter image in the catalogue so it's not that accurate, but I have both inboard & outboard versions I could email if you want. I love the Overniter design and I think the tumble-home stern really suits it. Hope we can see it in the wood eventually!
Gary

Planning a whole fleet, but starting with a Zip...I think.

"Just when you think you've made something idiot-proof, someone builds a better idiot!"

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sproggy
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Re: Barrelbacked Overniter Build in UK

Postby sproggy » Wed Apr 26, 2017 12:25 pm

Thanks for the offer, Gary, but I took dimensions off the plans and entered them manually into DelftShip (quite a tedious process converting inches and fractions into decimal feet for each one!) at each frame so my representation is probably more accurate than your scanned one, at least where it matters for the changes I've made.

All the frame profiles are now transferred to paper so the need for DelftShip has passed - the only function it serves at this point is for me to look at the renderings at least once a day while I wait to have two working shoulders again! Next job is to transfer from paper onto plywood and work out the frame inner profiles in the process because the full-sized Overniter plans give only the outer profile. I should be able to do that soon - next few weeks I hope. Transfer paper and tracing roller are at the ready! All I need is the physical ability to re-arrange the garage first to make some working space. I foolishly had a load of plasterboard (sheet rock/dry wall for our American friends) delivered while I was incapacitated and that's not light stuff to move..... In the meantime I'm already designing possible deck layouts (including a 'sedan' version) for a boat I haven't even started on the frames for yet :D

Ian

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sproggy
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Re: Barrelbacked Overniter Build in UK

Postby sproggy » Wed Apr 26, 2017 12:47 pm

I meant to ask - how are your plans coming on Gary? Are we going to have an explosion of Overniter builders in the UK? I believe there's someone on the south coast starting to build one too.

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gap998
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Re: Barrelbacked Overniter Build in UK

Postby gap998 » Wed Apr 26, 2017 3:54 pm

Still procrastinating on the house work I'm afraid and the hours on my new job aren't helping - been offered another position so that may change. I'm flip-flopping on what to build - after looking at the Nimrod, I decided it would be a better option than the Zip, both for my use and to sell on. Even modeled a barrel-back version: -

Nimrod-Barrelback.jpg


However, just got back from a canal holiday and I'm beginning to yield the wisdom of going straight for something bigger at the start. (yes Bill & Carl, you told me so). Thing is, I'm itching to get on the water and the physical & financial time-frame of what I want to build is frustrating. Toying with a 50s centre cockpit canal cruiser look-alike based on a stitch & glue hull at present. Unfortunately Glen-L's hulls are too beamy for the canals. Selway Fisher in the UK do some designs, but they're less polished & not very pretty... In any case I still have to finish the house before starting and explain to the wife why I spent 120 quid on plans I'm not going to use! :lol:

This is my inspiration!
Tamburo Starboard.JPG
Gary

Planning a whole fleet, but starting with a Zip...I think.

"Just when you think you've made something idiot-proof, someone builds a better idiot!"

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sproggy
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Re: Barrelbacked Overniter Build in UK

Postby sproggy » Thu Apr 27, 2017 12:40 am

Well you won't be moving one of those around the country on a trailer and launching it for day trips.... Not really my thing - I'm not the speed freak I used to be but canals are just too slow for me, although I can see the appeal if canals are your preferred waterways. The Overniter will fit on canals....just. Not quite the same level of accommodation, though!

Can you really do something that large with stitch and glue?!

It's true that many of the Selway Fisher plywood designs are less elegant than the Glen-L ones. I quite like their cedar strip Lobster - it is 'pretty' but not the style that I want to build.

Good luck with whatever you end up building, whenever you get the chance.

JaTro
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Re: Barrelbacked Overniter Build in UK

Postby JaTro » Thu Apr 27, 2017 4:52 am

I feel your pain,
so many possibilities, each has its advantages and disadvantages.
Althoug i bought house with garage last year, only now i realized that nothing bigger then Flying Saucer will be hard to squeeze in.
Its hard to decide which way to go. Wood or aluminium, trailerable or something bigger. So many dilemas.
Did you saw Wes Farmers Elco 26?

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gap998
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Re: Barrelbacked Overniter Build in UK

Postby gap998 » Thu Apr 27, 2017 3:31 pm

Haha - I wasn't planning on building it quite that big (it's 33ft x 6'10" Beam) - just styling along those lines Selway have a S & G hull 20 x 6'10" which could also pick up her skirts when not on the canals, but like I said, it's not pretty. Elco 26 on the other hand is though JaTro - Still too beamy for 7' locks though I think.

Glen-Ls Tug along is very narrow-boat-esque, but scaling down beam & stretching S&G is a bit of a minefield even with CAD.
Gary

Planning a whole fleet, but starting with a Zip...I think.

"Just when you think you've made something idiot-proof, someone builds a better idiot!"


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