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Thoughts on my dinghy design

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    Posted: 10 Aug 2018 at 11:17pm
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I have drawn up a 3.5m aluminium dinghy in solidworks so all the flat patterns can be exported for profile cutting. I already have a 30hp Evinrude to power it. 

3500 Long
1850 Total width
1450 Inside gunwales
700 From keel to top of gunwale
50mm wide chine down turned 10deg
13 deg deadrise at transom 

Download the 3d pdf of it and let me know what you think of it

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Post Options Post Options   Likes (0) Likes(0)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2018 at 11:58pm
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are you sure you want a length to beam ratio of 2:1?
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Post Options Post Options   Likes (0) Likes(0)   Quote quattro Quote  Post ReplyReply Direct Link To This Post Posted: 11 Aug 2018 at 11:54am
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Originally posted by Bounty Hunter Bounty Hunter wrote:

are you sure you want a length to beam ratio of 2:1?

Not entirely, its easy enough to change, this one here I have lengthened to 3900 and the width is 1400, also taken the gunwale right to the front, weight is 117kg, all 3mm 5052

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Post Options Post Options   Likes (0) Likes(0)   Quote JustAnotherSpearo Quote  Post ReplyReply Direct Link To This Post Posted: 12 Aug 2018 at 8:32am
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Have just walked into the garage and mesaured up the little bathtub. 
It is 3800 length 1660 width and is extremely stable given it is not a pontoon styled dinghy, I believe it has 10degrees deadrise

URLs don't seem to be working for me, so i'll just ask. Are you looking at having chines to help with stability / make things a little drier? 
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Post Options Post Options   Likes (0) Likes(0)   Quote quattro Quote  Post ReplyReply Direct Link To This Post Posted: 12 Aug 2018 at 10:41am
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What make is your bath tub?

Yes mine has down turned chines

Try this link, you will need to download it and view it in adobe

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Post Options Post Options   Likes (0) Likes(0)   Quote macka2012 Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug 2018 at 8:50am
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Are you going to incorporate any storage or anchor locker? The transom looks quite low too.
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Originally posted by macka2012 macka2012 wrote:

Are you going to incorporate any storage or anchor locker? The transom looks quite low too.


Yes there is a bulkhead that goes up the front. The transom looks low because it's 15" to suite the motor I already have otherwise it would be 20"
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Post Options Post Options   Likes (0) Likes(0)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug 2018 at 11:04am
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What's the intended use?
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Post Options Post Options   Likes (0) Likes(0)   Quote quattro Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug 2018 at 12:49pm
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Quick solo missions mainly
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Post Options Post Options   Likes (0) Likes(0)   Quote CrayZfish Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug 2018 at 12:53pm
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Just a thought. 3mm seems heavy for a dinghy. My 5m homebuilt is 3mm in the hull and is rigid as any similar size alloy i have been in.
Why choose either diving or fishing when you can do both. Besides crayfish tail is very good bait!!
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Post Options Post Options   Likes (1) Likes(1)   Quote quattro Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug 2018 at 12:56pm
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Its just for ease of welding and nesting all the parts together. 

In 3mm it weighs 103kg
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Post Options Post Options   Likes (0) Likes(0)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug 2018 at 2:59pm
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Originally posted by quattro quattro wrote:

Quick solo missions mainly


Doing what? E.g. fishing, diving, birdwatching ...
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Post Options Post Options   Likes (0) Likes(0)   Quote quattro Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug 2018 at 3:34pm
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Fishining, setting nets and long lines
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Post Options Post Options   Likes (1) Likes(1)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 13 Aug 2018 at 4:25pm
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Originally posted by quattro quattro wrote:

Fishing, setting nets and long lines


I can't get the downloaded file to open in my PDF software, so I'm commenting blind but here are some generalisations that may be helpful ... or not.

Freeboard is an important consideration for you.

You have a 15" shaft engine. That doesn't mean your whole transom needs to be 15" - just the middle third where the outboard clamps on. 

I would make the outside sections of the transom higher if possible.  If you end up backing down on a longline against the wind, then you will appreciate having more transom.

+1 for gull-wings or reverse chines for stability at rest.

Think about your bow design when it comes to setting nets. If you set the bow up up right - smooth, rounded lines and no sharp corners with shelf for a fish bin,  you can fire the buoy warp and pick over the front end and back away letting the net run out over the bow of the boat.  I used to find this very handy when setting nets in little rocky guts for Butterfish and Bluenose, or along particular features like channel edges for flounder.  The wind isn't always on your side.
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Post Options Post Options   Likes (0) Likes(0)   Quote quattro Quote  Post ReplyReply Direct Link To This Post Posted: 14 Aug 2018 at 5:36pm
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Thanks, I have a pretty much where I want it now, got a price of $2100 for profile cutting and ill do the folding at a mates sheetmetal shop, should work out nice and cheap for a new boat
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Post Options Post Options   Likes (0) Likes(0)   Quote CrayZfish Quote  Post ReplyReply Direct Link To This Post Posted: 14 Aug 2018 at 6:34pm
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Laser profiling or water jet? If you have a cad drawing its very easy to get quotes suggest might be worth looking round
Why choose either diving or fishing when you can do both. Besides crayfish tail is very good bait!!
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Post Options Post Options   Likes (0) Likes(0)   Quote quattro Quote  Post ReplyReply Direct Link To This Post Posted: 14 Aug 2018 at 6:37pm
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Originally posted by CrayZfish CrayZfish wrote:

Laser profiling or water jet? If you have a cad drawing its very easy to get quotes suggest might be worth looking round

Plasma cut, using a local company as any difference in price is lost in the freight cost
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