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C17 new project.

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    Posted: 06 Jan 2020 at 5:26pm
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Platinum
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 2020 at 9:45am
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Titanium
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That is so much like My dad old 14' 6" (think it was) kauri clinker boat with 25 hp seahorse from the 150s/ early 60s.
 Used to from KK bay and other places, out past Rakino, up around the Harbour bridge..Noises,  well out into the Furth..
 Towed with a Hillman Mix
 Saw some rather narrly weather , coming in well after dark as weather forecasts then where by Balloons, and they traveled west so much of the prevailing data was from Aussie and obsolete.
So they made solid design Sea boats back then.

I always have a spot spot for these old school type boats.
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 2020 at 5:04pm
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Platinum
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Old school design and hull shape. The C stands for classic.

The engineering is anything but old school.

Hull panels, frames and stringers will be Meranti. Superstructure Okoume.

Glassed both sides with 400g double bias and WEST epoxy.
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Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 2020 at 5:29pm
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Titanium
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Looks fab love the lines.

What trailer/motor are you thinking of?  Will you buy new or secondhand, will you make trailer yourself?
Good fishing trip nothing breaks, great trip catch fish.
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Platinum
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Image of frame explanation to follow.

Mac: Rated outboard is 50hp as designed. She should go 25mph with that with a full load of five adults. In the designers words 60 or 75 is fine 90 is getting dangerous and 115hp is excessive. I’ll see what is available when the time comes. If buying new will go a 60hp.

I am cutting the transom at 20” and wide enough for a kicker. I have a 2.3merc two stroke that will work.

Trailer likely to be multi roller. I’ll sort that out before the sole goes on so I can line up the reinforcements with the rollers.

6mm Meranti with biax both sides is stronger than the standard 8mm glass layup especially if you look at long term fatigue so rollers shouldn’t be an issue.
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 2020 at 10:28pm
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Thought I would post a bit on how to draw the frames as there might be some interested. Old school boat building has a table of offsets, which need to be lofted full size. That is because the designer draws the plans on paper, and when scaled up 30x the width of the pencil can be inches wide!

Modern plans are done with CAD and the lofting is done on the PC to far more precision than required for this method. In my previous dinghy I had some gaps of over 10mm to fill with epoxy putty. No issues other than cost and weight. I am aiming to do a better job this time. 3mm (1/8th") is the precision of the plans. No more is needed. 

To draw a frame start be drawing the baseline and Centrelines on a sheet of ply. The centre line is the centre of the boat (vertical pencil line) the baseline is (in this case!) the top of the solem marked in red vivid. All measurements are taken from the CL and BL unless stated.  It is IMPERATIVE that these lines are perpendicular! I measured against the edge of the sheet multiple times over the line.

For tools I used a rafter set square, a fabric tape measure and a standard builders tape. The fabric tape measure is best for quick checks of distances along the sheet. One can use another sheet of ply as a straight edge and right angle if needed. The edges should be very close to square from the factory, but always check.


This frame is E (last frame in front of transom). It will form the motorwell bulkhead, reinforcing the transom and preventing swamping from waves over the stern. 

I measured left of the CL 822mm then directly down 70mm. Drew an X in pencil. Then up 641mm from BL and left 1015mm of CL. Repeat for the other side. Draw in the boundary in pencil then over in vivid so I can see it more easily when cutting. I found in my previous build that when holding something that will have your fingers off in a second you don't want to be losing the cutting line.

The top of the frame has a slight camber (curve) in it. This is a parabolic shape drawn by putting a batten through three points shown on the plans. The curve is for the side decks later. A batten is a really effective way to draw a nice fair curve. I'm using an Aluminium flat bar on edge from Mitre10, but anything that will bend with little effort in a fair way will work. Hold the batten down on three points and draw the line in pencil. The flat bar also makes a very useful and cheap straight edge. It will end up on the keel or rubrail later on. 

Easy as, just take your time and measure measure measure. 







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Platinum
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Profile picture. 



I am cutting the outboard well wider. That will mean not as much storage near the transom, but room to hang an aux without using a bracket. My 2.3hp two stroke will manage (shaft length 17"). The rest of the transom area will be boarding platform and flotation compartments. Drainage will be through elephant trunk scuppers RIB style. 

I am planning to cut down the rear panels to meet the transom, similar to some more modern designs. I think it looks good as designed but would much rather have easy access to the rear for hanging the aux if I ever need it. 



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Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 2020 at 6:37am
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Titanium
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thanks for the replies interesting.  Have you considered saving a search on trade me for an outboard used in case a suitable one turns up?
Good fishing trip nothing breaks, great trip catch fish.
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 2020 at 8:40am
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Wee while off that still. I don't want to have an outboard lying around for possibly years while I finish her. I do keep an eye on TM though I don't want to put a cheap ass motor on a once in a lifetime project. 

I would like to get it in the water summer 2021, but that depends on being able to use all my holidays on her. I am a teacher so that helps.
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Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 2020 at 9:05am
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Titanium
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Originally posted by OneWayTraffic OneWayTraffic wrote:

Wee while off that still. I don't want to have an outboard lying around for possibly years while I finish her. I do keep an eye on TM though I don't want to put a cheap ass motor on a once in a lifetime project. 

I would like to get it in the water summer 2021, but that depends on being able to use all my holidays on her. I am a teacher so that helps.
Sure once you are getting there start looking - 6 or more months out is good to save a search by all means new if that is what you want, if buying new or used wintertime is a good time to buy as market quietens down - in my experience Dec/Jan/Feb usually crazy at boat shops.
Good fishing trip nothing breaks, great trip catch fish.
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Titanium
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What total gross weight with ppl etc do you recon it will be on the water?
 What speed do you realistically recon it will get over the bow wave on the plain?
 Havnt done this sort of old school hull or looked into them.
 It is a plaining...yet,. going of my dads old clinker 25hp @the powerhead.. not prop.. it was more a displacement to semi displacement, which is a total different kettle of fish in calculation.. formula.

Messed with some planing hulls trolling as displacement , semi displacement.. defiantly hull length a serious factor.

Would like to play with some numbers. I have no accurate data base of similar hulls to even estimate hull constants on the plain.
I would certainly not take the results as anymore than a very generous ball park.Ermm



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It's a constant deadrise planing hull. 45 degrees at cutwater, but 10 degrees at the transom. Very very similar hull form to the Tolman skiff. Almost exactly the same deadrise chine width etc.

The study plans have the Designed Water line at 682kg. I think that's a little optimistic if all five in my family are on board. We will see how I build it. I figure 600kg if I am alone, 850kg+ if I have passengers on board. 

I know that several of these have been built and easily done 25+mph with a 50-60hp motor and several adults on board. Stepping up to 70hp is a fair bit more weight on the transom. 




(Edited deadrise. Closer to 10 than 9.)


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Post Options Post Options   Likes (0) Likes(0)   Quote otdrmn Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 2020 at 12:05pm
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Nice, check out the otdrmn YouTube channel for a pictorial video of the first OB17 being built ,also by bateau boats
The 4 R's ~ Rods, Reels, Rifles, Rooting
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Titanium
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 very ball park stuff
Say 690kg (assume includes motor gas batteries etc)  plus several  lets say 2 ave 80kg  say 850kg total.
say 55hp 25 mph
Gives a hull constant around the 145...which would at a guess would be a little high but certainly on the high side of ball park.
 Interesting.
 A lot would depend on construction...ie dont get too carried away with too many glass layers  .. go over board.
I was looking at a wood over ply boat the other day, some 50yrs old, similar construction ('little toot' nic named) bit bigger.. glass mat over ply over ply with polyester resin. Still as solid as the day made..and not over board on the glassing..
 The builder in trade..no filling between joins..again that starts to add weight..
After the 1st 'practice' project this Im sure will come out really well...

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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 2020 at 5:12pm
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Glass resin ratio is another. Good hand layup is 50:50. New guys get 33:67 often as not. That’s twice the resin for no gain in strength. I’m not sure if the hull weight quoted is for Meranti or Okoumé. That’s a 40kg delta easy. I’m using Meranti for the structural stuff Okoumé for interior parts.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 2020 at 5:38pm
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Titanium
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Good hand layup is 50:50
 Back when most of our lay up was poly and 95% chopper gun we weighed out resin and rovings 3:1
Light hop strand hand laid depending on weight and day humdity/ temp a little heavier and heavy C strand getting up to 1:1
 Cloth was far easier to wet out and roll so that was close to the chopper gun.
 Chop stand type issue .. dont know if you will use that.. used to lay up behind gelcoat when mould making was far better than 3:1

 Yes ratio backs a huge different to strength and weight.
 Back then epoxy was imported (Muldoon days) very very expensive and very rarely used.

I see these old glass over ply very well made poly resin boats and old glass boats from workshops like lotus, Sea nymph, Haines still around these days in excellent condition...I do wonder about why the extra expense/ weight of epoxy.. yes it is stronger but is that strength and durability in engineering terms required?

It has been debated before .. but just a thought to consider maybe.
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 2020 at 7:09pm
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The designer (Naval architect with 40years experience) specifies Marine epoxy and wouldn’t condone polyester. The engineering relies on it. Weights the same cost differential is about 2% of the whole project. I am not aware of any modern design that specifies polyester in this type of boat.

Maybe for a ply on frame build with the strength in heavy framing and fasteners. Even then I would use epoxy as the amount in such a boat would be very small.

In this build I’ll use only the best materials available for the hull.
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 2020 at 8:29pm
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Originally posted by otdrmn otdrmn wrote:

Nice, check out the otdrmn YouTube channel for a pictorial video of the first OB17 being built ,also by bateau boats

Nice work. Did you build that? Do you still have it?


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Post Options Post Options   Likes (1) Likes(1)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 2020 at 9:56pm
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I asked him that. He sold it. That was the first OB17 built. Many others built since.
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Titanium
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Weights the same cost differential is about 2% of the whole project....
....Maybe for a ply on frame build with the strength in heavy framing and fasteners. Even then I would use epoxy as the amount in such a boat would be very small.

Thumbs Up
I understand that on a boat that size..no bulk heads etc.
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