Building a ply dinghy.

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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 21 Aug 2017 at 4:39pm
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I think your 1st coats was enough.. if didnt have wrinkles/  plastic on it. That would just needed a good block off , not going thru, a hi build epoxy undercoat , blocked off and finish coat.
 You now have 2x thickness , lot extra weight...think of the 2nd coat as a hi build under coat that needs blocking back.
 So another coat should not be required, and maybe a hi build should also not be required before final coat.

 What ever you do.. when you see the layer to the underneath get thin, do not sand further.
 You can not sand out a hollow, but you can build it up with a high build undercoat .. If have not gone thru... thin is ok.
 These basic methods/ principles apply to prepping a high end show car for the perfect mirror finish.
And plastering a wall or ceiling perfectly flat so imperfection dont show up when light is cast down the surface
 Yes have done both more than once in my time

using a disk sander(if required) then  DA and/ or belt sander, then finish with a long board is the fastest , quickest, least effort, to creating the perfect finish.. and the difference between 'acceptable' and perfect is only a few minutes work. Yes a few minutes....
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Post Options Post Options   Likes (0) Likes(0)   Quote Don18025 Quote  Post ReplyReply Direct Link To This Post Posted: 21 Aug 2017 at 6:14pm
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Oneway, I m trying to work out why you applied that thick heavy home made coat on your hull. 
First rule of dinghy building, build it light. you added enough extra weight with the glass cloth. Then you put the thick stuff on. Your boat is not going to be a super yacht rocket ship so does not need extra protection or the finish that may have promised
Second Rule; use a good oil based house paint over a useful undercoat - job done. I have applied Resene undercoat for fibreglass over ply and then an exterior top coat, has lasted 12 years and does not need a repaint.
An observation; that skeg looks like a waste of time, first rock you hit will break it of. It will make the dinghy weather cock or end up being pushed by the current at the stern. A skeg tapering forward about 2/3rd length of the hull will strengthen the keel area and should   give good direction control. 20mm high near the bow and 80 to 100mm high 300mm forward of the transom.

You have done really well so far so get the finishing right and it is very simple.
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Post Options Post Options   Likes (0) Likes(0)   Quote viscount Quote  Post ReplyReply Direct Link To This Post Posted: 21 Aug 2017 at 7:23pm
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Use a DA with 80 on it and sand it back smooth, you needed a good squeegee to put plastic or peel ply
Calling fishing a hobby is like calling brain surgery a job - Paul Schullery
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 21 Aug 2017 at 8:04pm
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Don I should probably explain a bit. 

The boat will be mainly used for crossing salmon fishing rivers and trout around lake edges. The bottom will be getting a bit of wear and tear, as the boat will get dragged up rocky or sandy beaches on a regular basis. If I was using it to go to a mooring I wouldn't bother. 

The info sheet for Westsystem 420 aluminium powder says this: 

Aluminium powder is added to increase toughness and to shield the substrate from ultraviolet radiation. Adding between 5% to 10% of 420 Aluminium powder by volume will provide protection from ultraviolet light in areas which are not protected by other coatings. For this reason it is often used as a base for subsequent painting. The additive will also substantially increase the hardness of any coated surface.

That sounded like goodness to me. American builders usually use Graphite powder instead for scuff resistance and UV protection. I did not really want to paint the bottom as I figured I would be scratching it too much. I do not mind if the coating is a little thick. Weight will not be a major concern for this dinghy. The total weight (30-40kg) will be well under the recommended load (100kg) of the beachmaster dinghy wheels I intend to fix to the back. 

The extra use of epoxy is another thing, but I bought 12litres when the BOM said 6 would be enough (for a careful builder keeping material use to a minimum.) No matter how much I waste, I expect to have some left over sitting unused until the next project. 

Possibly the coating is overkill, but I would rather overkill than underbuild. I never seriously considered a fairing cream for the bottom as some use as I wanted it to be as tough as I could make it. If I had access to and there was an easy way to coat it with UHMWPE I would have used that instead. 

I don't mind sacrificing looks for utility. I am aiming for a practical finish, but I don't want it to look like it was built like somebody who doesn't give a damn either. Does that make sense? When done I want someone to look and think that it fits perfectly the use to which I intend to put it. 

The skeg isn't finished yet. I stuck it on quickly in the morning before going out with my family. I was given 20minutes (timed) to work on the boat and wanted to get it on while the epoxy was still green so I could get a chemical bond. I used two layers of 20mm pine. The plans state a rounded triangle 450mm long and 80mm high near the keel. 

The designer definitely knows his stuff. I intend to cut it down at the front and possibly use the cutoff bit to build it up at the back. With my tools at home that was easier for me to do. 

I don't want to sound defensive here; your constructive criticisms are truly appreciated, and preferred to pats on the back!
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 23 Aug 2017 at 12:36am
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I had a wee play with the skeg today. I could lift the boat with it. Epoxy has a tensile strength of 50MPa. That's roughly 5kg per square mm. Multiplying by the surface area of the skeg and the surrounding glue fillet and that's several tonnes! Should stay put.

I do need to pretty it up some and curve off the ends. I was also thinking about a bit of Aluminium strip on it, not sure if that's worth the time and bother?


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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 24 Aug 2017 at 10:24pm
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Today after work I cut out the rubrail from the original sheets of plywood. I used the hull panels as a template before stitching so the strip followed the hull perfectly. Not my idea but works a charm. Thin coat on the ply then thicker coat to bond. Used leftover glue mixed with west420 to feather in the sides a bit.
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Post Options Post Options   Likes (0) Likes(0)   Quote Don18025 Quote  Post ReplyReply Direct Link To This Post Posted: 25 Aug 2017 at 7:51am
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Oneway, that looks a really smart dinghy. Like the sheer line.
Really good effort to date

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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 25 Aug 2017 at 8:45am
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Plan for this weekend is to sand down the bottom and stick on the second layer of rubrail.

Next weekend I am hoping to splash it in Pegasus lake to test stability etc.
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Used my sawmax and multitool to cut down the edges of the rubrail then over both sides with a round off router bit. Sanded the bottom for a couple of hours at least. Rounded off the skeg and coated with epoxy. The pieces of wood you can see I'm bonding to the back will be for the beachmaster wheels. I'll attach the wheels to a ply bracket glued to that wood. Should be better than drilling holes in my boat, letting water into a sealed compartment.
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 27 Aug 2017 at 7:29pm
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After sanding the hull down both by hand and with the multi tool I put another coat on. Covered sides and bottom, special attention given to the bottom of the rubrail which got two coats of neat epoxy then brushed over with a thicker mix.

The finished product is much better than last week. I may paint the bottom or I may not.
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 27 Aug 2017 at 7:34pm
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Time to consider paint. A google tells me that many speak well of dulux weathershield. However that is an oil based paint overseas while in NZ it's a water based acrylic. Aside from a exterior house paint I was also looking at Toplac. Price is similar from marine deals. I won't need to prime; the epoxy does that but I am not sure if I need an undercoat or not. Toplac says nothing about undercoating that I can see.
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 29 Aug 2017 at 9:15pm
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Beachmaster dinghy wheels arrived today. Those things look solid. Nothing like the cheap plastic jobs. 5mm Aluminium frames, stainless connectors and plastic just to keep them seperate. 

I need to cut a ply bracket for them and glue it to the wooden supports bonded to the back. 

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Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 30 Aug 2017 at 7:39am
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Looking good want to see pic of first fish caught!
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: 30 Aug 2017 at 3:00pm
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I can tell you already that it won't be a tuna or a Marlin. Hopefully I'll get into the salmon as Christmas nears.
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Originally posted by OneWayTraffic OneWayTraffic wrote:

I can tell you already that it won't be a tuna or a Marlin. Hopefully I'll get into the salmon as Christmas nears.
first fish I caught with new boat was an eel!  Wifey wasn't impressed or game to eat it.  Luckily boat redeemed itself later.
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: 02 Sep 2017 at 11:51pm
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Put on a couple of cleats for gluing the rear seat, cut out the mid seat frame side and glued that in as well. I may or may not do a bit more on it tomorrow and will post pictures then. 

Any thoughts about outboards? Better weight under 20kg, which leaves one of the 2hp outboards. 2 or 4 stroke makes little difference either way. Was favoring a Honda 2hp due to the lack of a waterpump but I have heard horror stories about corrosion in the salt for that one. Apparently it's a lawnmower engine with too many mild steel parts.

That leaves the Suzuki 2.5, Tohatsu 2.5 or 3.5 2 or 4 stroke, or the little Yamaha 2stroke 2hp. 

Anyone got any experience with any of these engines? 


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Post Options Post Options   Likes (0) Likes(0)   Quote Dagwood Quote  Post ReplyReply Direct Link To This Post Posted: 03 Sep 2017 at 7:54am
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Must be a serious number of those 2 stroke Yamahas out there being abused as tender outboards. We had one when I was a young fella some 30 years ago and they look unchanged. Cheap, simple and reliable.
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Post Options Post Options   Likes (0) Likes(0)   Quote Tagit Quote  Post ReplyReply Direct Link To This Post Posted: 03 Sep 2017 at 8:40am
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If you want toughness as well as an excellent finish I would suggest using Perfection rather than Toplac. Perfection is super hard and about as tough as a paint finish will get. Will take probably one more coat to finish than Toplac as it applies in thinner coats so a little more work up front.
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 03 Sep 2017 at 9:40am
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Already ordered Toplac. My main concerns with the two part paints came down to smell, cost and the fact that they would highlight every imperfection off the finish
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I have used Toplac and Perfection. I love Perfection because of it's toughness but Toplac is easier to use and like Perfection does a great roll & tip finish if that is the plan.
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