Sea Sled Madness: It's Incurable

With the guidance of you fine gentlemen I will probably design another sled, using the TX18 as my starting point. I'll put if off as long as I can, but our commuter leaks a gallon an hour. It will have a last day. We can't use Serenity as a commuter for Anne, so a second boat is required. So here we are.

Can anyone recommend good "unwrapping" software? I can draw something but to get plywood shapes for stitch and glue construction I would have to frame it up, and skin it with cardboard.

 

That can be done with AutoCAD and Fusion360 on the inexpensive side. However, kind of a steep learning curve if you aren't used to drafting. You will doubtless still have to loft from the flat patterns so I wouldn't make them too ambitious. For instance, if you did a complex elliptical shape for a chine, you'd have to use a rather large format printer to print it out. A video projector isn't a good idea either as you'd distort the drawing. However, there may be some boat specific software that I am unaware of.

I guess what I am saying is once you get these flat patterns you would then need a way to get them full size onto your cardboard or plywood or whatever to construct your craft.

As an easier way to maybe consider doing it... Work out your lines, aka where your frames will be just like you were building a framed boat then you can get the big plastic they use to template boat canvas I use one called Pantex ... its a woven polyethylene and it doesn't stretch and its clear. you can then staple that to your wooden frames and use a sharpie to make plastic templates that will then make your flat cutouts. This way you could still use some computer software to determine the frames if you wanted to mess with the hydrodynamics and what not. Once you're done the wooden frames will be flat and the plastic will roll up so you'll have easy storage and can reassemble your model if you want to make changes.

 

If I may bring up that old chestnut again, what have you established so far in the Statement of Requirements for the new sea sled?

And how will it be different to the standard TX 18?

 

Indeed.
Can't run before you can walk...
Must get the SOR and then must turn those simple sketches into a proper scaled dwg with real weights.... all based on the SOR.

If you don't do this first.... it'll end in tears...and an empty piggy bank!

 

Mertens, at some point had Orca for Rhinocerous, iirc. He could not afford to keep it active, so he ran all of his boats through the software at some point, but, of course, never ran hydrostatics that he ever publicized. He probably verified them is all; more or less. He was already a well established drawer of boats.

The software does what you ask, but is cost prohibitive for the design of a single vessel. Worse, for a simple modification like adding a pilothouse and reworking the numbers; too costly.

I think Delftship is free to mess around with and then maybe $300 to actually get hydrostatics out of; so unless mistaken; it seems like an affordable option.

And, I think you could put the TX18 into it and get accurate detail to do the modifications you desire without building a hull that won't let the engine make her wot rs.

I really like Mertens PH22, but had asked him to draw it as a PH24 and expand the trailering bit(beam) from 8'6" to +10%. I even offered to pay and got crickets. He is over 70 and retired and likes to travel around on his boat, so I can't say as I blame him a smidge.

If you try to mess with Delftship; let me know; maybe I'll get the PH22 plans and modify in the software to my plus 10% all around. I hate the back of the boat internals as drawn anyhow. My wife may think I've lost my mind, so if you stop hearing from me, she probably has cut off internet access!

I think Bajan and AH are not wrong. While you may have an SOR; you need to be careful the SOR does not affect the plan, which I think you are on the right track now asking about software. So, they may have forgotten the sor exists with your latest drawing is all. Or, they may both recognize your shifting wishes for this boat have gone from a dry commuter to now running many bundles of shingles and are wondering if the TX18 is the wrong boat completely. And to be fair, when you first asked about a cabin; I thought u meant for two people; not four, and I have been paying some attention. Personally, I think you can pull off a small hard cabin, but not forward and maybe not for four if the back is closed.

I don't know if delftship does things like internal or general arrangements..

 

Guess we are not talking about the demands calling for a complete 3D Cad installation (I use CadKey/KeyCreate for hull modeling). Granny's method is to draw on paper and then make a triangular mesh based on a set of stations. Then all the triangle "legs" can be calculated by the 3D Pythagora's method, using the x-y-z coordinates. These lengths are then directly carried over to the flat panel, and the nodes connected by a smooth line (some transfer the dimensions to a X-Y grid, but that's waste of time and may cause loss of presicion). You can set up an Excel sheet to do it without bothering with Cad software.

• There are some free/shareware mesh unfolders available for origami enthusiasts, that do exactly this. Iirc one was named "pepacura" or something similar; Google has the answer....
• Look under the Boatdesign Directory>Software>Free "something". The Carlson design is doing what you look for, and its file format is accepted by the FreeShip software.
• If you draw on paper, you can import the chine coordinates directly into FreeShip as a tabula in a simple text file, and from there you get the rollout shapes.
• Personally, I am not comfortable with the way the spline control points are manipulated in FreeShip, and prefer the old "Hullform" software; it works the way my old boatbuilder's brain does......

The upside with FreeShip (and DelftShip Free) might be that there are forum members that are very good with their use.

 

Thanks fellows. It certainly won't hurt to restate the SOR.

1 Fits within an 18' by 8' 6m by 2.4m envelope.
2 Hard cabin for four, good shelter in freezing rain and general misery when the occupants are already cold, wet, and tired.
3 Hulls sides as straight and parallel as possible.
4 Bow square.
5 Power to be roughly 50 hp outboard
6 Must be able to plane with 1300#, 600kg of load.
7 Load will vary tremendously in magnitude and placement, so must be tolerant of loads off ideal LCM.
8 No particular speed is required, beyond #6
9 High roll stability under extreme off center loads.

#3,4 and 9 are about being able to load heavy awkward things from any point on the sides or bow without risk of dropping things in the water.

I didn't write "must be sea sled" but nothing else will do, so that's a given.

 

With the tunnel aeration issues/lack of prop traction on Serenity do you think that this major issue will disappear with a shorter hull

If you go with twins, you get redundancy and the props in greener water. If the stern weight is an issue, you might be able to increase your envelope to 8’6”
There are lots of cats running around with twins

 

I think the sor is good, with the exception of 7 which is something of an oxymoron.

I want a small 18' boat that is load tolerant is too open ended.

If you have four pax and 10 bundles of shingles; I hardly expect the boat to perform well if you setup an aft cabin and then load 700 pounds on the foredeck. I just don't see it..

The only way to achieve this is to build the boat in such a way so 6 of those bundles are aft.

But even hauling groceries; that boat isn't going to do well loading the foredeck. You'd be better off making a ducker head for the ladies and closing it off with 4mm ply.

In opposition to the build concept of Serenity; you build this boat ultralight to allow for some loading versus the idea it has a high immersion, so it doesn't matter.

And if you want to run too many bundles, you run with 3 guys and a starter course and send the 4th back to the truck alone for more.

My 2 cents while my truck warms up for a parts run. All the best.

 

.....item #2 means there should be a decent bar facility?

 

I would respectfully disagree - I am sure that a small power cat would be able to give a good account of herself re your intended SOR.

Have a look at this one - she fits within your dimensions, and has a maximum payload of 375 kg with two crew on board.
Ok, some of this would have to be subtracted for the weight of the cuddy / helm enclosure, but even so, she should still be able to carry a reasonable amount of timber or shingles and other materials (?)
Powercat 525 - The Multihull Centre https://www.multihullcentre.com/powercat-525-2/

Or even a slightly scaled up version of this 4.2 metre Ripple cat tender?
Tender Catamaran Kits | Tender Catamaran Plans | Ripple Tenders https://www.spiriteddesigns.com.au/ripple_tenders1

 

The aeration is an issue here due to two factors:

1. The prop shaft is ~2" too high
2. The standard propellers have no, or too little cup

 

??

A cat has less hull and lower immersion for the same beam/length which is the opposite of his goals for loading. If anything, he'd go away from the tunnel concept entirely in exchange for more loading.

If there were no slip constraints; the paradigm changes, but a cat is not the answer despite my affinity for them.

 

But surely it all depends on how much cargo he actually 'needs' to carry with the 'little' boat.
It could well be that 500 lbs is plenty enough for most situations (?)
If John wants the absolute maximum, then he needs a rectangular shoe box - but that won't go very fast.

 

Aah, but that's where the Sled fits in...... .