ISO Skiffmaran

Basic outline of idea:
Advantages of pointing / turning of a dinghy

Stability and space of a trimaran

Decent sail plan (ISO rig is pretty powerful: 14.3m main/jib with 18.8m asym spinnaker)

Cheap - ISO 949 with 3 sets of sails, road and dolly trailer, hull in great condition and a spare almost new mast £900. bargain.

Safe - I have lots of health issues that mean capsizing is a very bad plan. Long outriggers, wide beam to ensure I keep walking.

Flexible - sail single or double handed

Fast - the RYA PN of the ISO is 926. It is now an old design but I couldn't find anything better value for money with that sort of potential.

Light - easy to manouevre on land and step the mast single handed

Fun - has ability for single trapezing (or two if light which me and my wife are)
so huge righting moment
The outline is to cobble together a frame and outrigger to get some idea of dimensions, initially sail as a proa to see what is what (and while I make the other outrigger...). Once it is sailing fully, I can take a view on improvements and at that point am aiming to make a brand new replacement main hull based on the ISO/29er/49er sort of configuration using the outriggers.

The new hull will be stitch and glue ply with glass reinforcement.

For the frame initially while I get dimensions sorted, I will rivet it together before welding the final design.

The outriggers will be stitch and glue as I have done that before and it is pretty quick, easy and flexible. The first one will be a quick lash up and will almost certainly need lots of changes and refinement so no point in spending ages on it.

Once functional, I am planning on adding some simple foiling appendages for foil assist, not flying it.

This will be sailed initially in safe coastal waters in the UK near Lymington/Christchurch mainly, but further down the line I hope to sail it to / around the Isle of Wight and further afield.

The end goal in 5 years time is to possibly use it as part of an adventure sailing around the UK.

I will start adding some bits and pieces of pics of the build so far.

I think I've spent about 50 hours desiging and building it so far - this year has been far too busy with owrk and home projects hoping this spring to make huge strides with it.

 

First stage

The ISO dinghy is not overly common but cheap as chips here in the UK.

I have sailed various other dinghies and small catamarans although only recently converted to sailing and find it a really nice boat. It is quite tippy for me and my wife as we are both light, so adding some stability to it makes some sense while we get further skills and more used to it.

Here is a pic of it being sailed by the previous owners for those who are not sure what they are.

Quite a complex and very adjustable rig, so loads of scope for learning and improving overall sailing skills.

 

Outrigger build

The outrigger is made from mainly 3mm okoume ply, with internal bulkheds every 500mm, length 4.75m.

I have flared the shape so more bouyancy up front to help reduce pitchpoling.

I have made a very sharp nose to pierce thorugh waves and the bottom has a gentle V to give some immediate bouyancy (at the expense of added drag I know), but the plan is to be using body weight to keep the outriggers only skimming the water as much as possible.

Also I just like the shape and will be aiming for the same basic profile on the new main hull when that comes about (much further down the line).

I have attached a couple of pictures to show adding shear clamps, an indiction of the bulkheads in situ and the outside being glassed.

 

Looks like an exciting project! I like the look of the amas-how long and wide?
Keep posting your progress-I'm very interested in following.

 

More Outrigger Build

The inside was fully glassed and sealed and as I wanted to try out some of the paint colours for later on I painted it inside as well.

I like the dark blue but will probably end up with black (homage to Hugo Boss).

I show here the reserve bouyancy I have added in each compartment using large drink bottles and then various smaller ones to fill out the space and then preventing it moving by using some dabs of Mapei flooring adhesive and filling the remaining larger spaces with closed cell pipe insulation lengths. It adds very little weight and if something catastrophic happens it will ensure around 120kg of bouyancy in each outrigger.

I have then got the deck on in two parts (nailed with bronze deck nails and resin with filler) and glassed it so it is watertight. I just need to sand and paint it and add in an inspection hatch.

 

The outriggers are 4.75m long, just under 30cm max width (22cm at back) and max height 38cm tapering down to 32.5cm at the front and 22cm at the back.

 

Outlining the frame size

with bits of crappy of aluminimum just see how it would go together.

The ISO has detachable wings for lighter sailors like us that slot in nice and easily.

Once the frame is on then we on't need the wings so no problem if the mounting goes over the holes.

The frame will be removable with a bit of effort (undo 8 large plastic knurled knobs on the C Bolts and take out 2 long pins holding the frame in the middle of the cockpit) so it can revert back to the (almost) standard dinghy (albeit with some holes in the top of the gunwhales).

The frame in the boat is made from square section aluminium bolted to teh gunwhales using large C bolts and using plastic chopping board as a spacer each side.

It can also still be sailed with this in place, the wings can't quite fit on but not a huge problem at the moment.

The frame is angled up so there will be a decent gap between the trampoline and the sea. Lesson learnt from my Sport Tandem "Kaymaran" project where my nice curvy crossbeams leave the trampline quite close to the water.

I've put a couple of pics of that project in - one is clearer but the darker crappy one shows the main sail as well.

The frame is riveted together for now while I get final dimensions confirmed.

I need to put some more bracing on it but for initial testing this is sufficient.

I have turned the tiller around and remounted the extension so it clears the rear crossbeam. I took the chance to sort out the rudder mechanism which is quite clunky to make it smoother and easier to lock and unlock.

The water in Christchurch Harbour particularly is very shallow in places so it needs to be able to pop up and down easily and reliably.

The plan is to use 2 very long tiller extensions so they don't need to be passed around awkwardly. I will probably make these from plain ally tubing and will put a spade type handle on as my grip can be suspect due to spinal issues. I will then put on some larger foam grips to make it easy to hold and will put in place an oar lock type of holder on each side.

It will be used to leave the tiller in when on the other side so it can slide easily but also have the ability to lock when required so a course can be set and forgot. Looking to use something simple like strong velcro so infintely adjustable - have that in the cup and teh ability to keep the tiller velcor separate when it needs to slide by itself.

The frame doesn't get in the way of anything, I just need to do a very small amount of rerouting the rigging for the spinny and the trapeze bungees. Pretty trivial.

Leaves plenty of room to get around the cockpit and traverse from side to side.

 

Frame further info

Here is a picture of the frame showing the slot where the crossbeams will go in.

There is a large hole drilled in which is used for the fixing bolts that clamp the beams in place. It is a 10mm hole top and bottom which has a small piece of ally tube going through it and an 8mm bolt through that.

Doing that so not having the stainless and beams together in case of any movement mashing the hole - hopefully the tube will keep it tight and can be replaced easily.

This part of the boat was the subject of my question a few weeks ago about the fact that the ISO is not remotely symmetrical. The frame mounting points are 3/4 of inch differently positioned so it makes everything a bit on the skew. The frame itself is square and in line with the midline.

 

Crossbeams and outer frame

So the plan was to make the outriggers demaountable. I only have limited space for parking the dinghy at Mudeford so it can't get any wider than the main hull, otherwise I will need to pay a lot more for a multihull space.

So, the frame is made up currently of round ally tubing, using riveted box section ally to join it up together.

This shows it being mocked up prior to the outrigger decked and sorted. I had borrowed some bouyancy bags but when I realsied how expensive they are went the bottle and foam route shown earlier.

The tube slotting into the frame is reinforced with 5mm ally bar on the bottom and inside so it fits the box section frame nicely. When it is finalised I will use cutting board again so it will be smoother to slot in and out especially after it gets wet and salty. The ally bar will remain as a reinforcement to prevent flexing of the crossbeams.

The seconds picture shows this and the knurled knob for releasing the crossbeam holding bolt.

I am not sure exactly where I will mount the outriggers yet as I might take the rear 50cm off to shorten them slightly. I also want to drop it in the water and see if the vertical conenctors need altering before finalising those.

I will simply screw the flat ally / ply connector plates into the shear clamps and probably use a ratchet strap for safety when I drop it in and ill aim to take it for a quick spin as a proa to get an idea of how it works.

Once finalised, the flat plate connector will be screwed and epoxied in place and faired in. The vertical strut will become round as well, just easier for no wto botch in the square tube at 45 degrees so water will pass it more easily in the first test float test.

The weather here is turning nasty for the holidays and I still have quite a bit to do to it and laods of work on so might not get a test sail in bfeore February unfortunately.

I will put up some more info on the frame and trampoline shortly.

 

The Trampoline Approximation

I've bought the trampoline material and vinyl edging from Sanders Sails, eyelets from ebay and borrowed my neighbours sewing machine.

Good to go.

I have made it a bit over size on my first attempt while I learn how to sew and see how things fit. Guessing I will take at least 5cm off both length and width (assuming I keep the dimensions of the frame the same) once it settles into shape. I don't think it will stretch much, but assume there will be some.

Used strong double sided tape on the vinyl edging to hold it in place, attached it to the mesh then sewed it in place with stitching both sides.

Had to use a standard strong thread for now as had difficulty with the sewing machine not being happy with the thicker UV resistant thread. Once finalised I'll do it again or get a friend with a bigger machine to strengthen it for me. It will do for testing.

I then hammered in strong eyelets every 15cm or so to make sure the load is spread evenly.

Finally, I lashed the trampoline into place with bungees from my old gazebo but I think they are too stretchy and will degrade quite quickly. I will be looking to attach the trampoline finally to the demountable frame with 3mm line and then be able to quickly attach it to the frame on the main hull with a further 3mm line and quick cleat to make getting it on and off as quick as possible.

Basically fine.

Next thing, attach the outrigger and see how it looks.

 

its looking good
might be better to wrap the tramps over/around the frame. Looks as if the tramps will sink a lot with weight on them.
How much of a keel do the amas/floats have?
Almost time to get wet?

 

Spectacular!
Love your project.
Please keep the build progress coming in this thread.
Not to add to your workload maybe some pics o fthe bottoms of the amas and the details of the bulkheads where the crossbeams attach to the amas.
Three hearty cheers,
Tom
PS - thanks for the nice large format pictures... can see details great.
Except - cant't quite make out what the K reg car is in the garage (what we call it here in the USA).

 

thanks for comments

This is all mock up to get dimensions correct at the moment. Once I am happy I will be bending and welding up the frame.

The tramps will also go over the frame in the final edition as well to ensure it is lifted.

I have just moved the mounting points on the floats forward 50cm as I will shorten the float by 50cm for better balance.

No keel as suck on the floats, I will put up a picture of the underside.

I'm actually about to head out and plop it in the water this morning to check levels and test if the small electric trolling motor has enough to move it around and how long the battery might last. Just made an easy slide on attachment method for the floats and got a bit more epoxy on them yesterday.

There is a really tricky entrance to Mudeford/Christchuch harbour with 6 knot flow in a really tight space so having some support if the wind is not great is almost madatory as tacking almost impossible.

The white K reg car in the garage is a Triumph Stag - which was a wedding present for my wife. I rebuilt it secretly for her and prended to have borrowed it from the Triumph club for the wedding. It was her dream car so she drove it forthe day (so I could dirnk!) and it was very funny when taking photos splashing through a local ford as she said "I don't want to do it the owner will get really upset").

I opened the wedding speech with "I have been lying to my wife for 6 months" - everyone apart from her knew, but the look on her face suggested I should explain quite quickly... Original 3.0 litre V8 which is actually a brilliant engine when sorted but I swapped the standard 3 speed auto box for a Jag 4 speed which is fantastic - it cruises at 80-90mph all day loaded up with gear barely ticking over. We've been camping all round Europe in it. The other green one under the cover that appears in some photos is a Morgan Plus 8, rather tuned up that goes like the clappers.

Will hopefully have some useful photos / feedback from trip this morning before work kicks back in for the rest of the month.

 

So, it's is a Morgan, and a V8 at that. Clappers sounds about right

I'm not sure I get your plans for using the frame assembly, so I'll pass on my experience with an old Newick Tremolino I had for a while... when in use, the complete frame structure, including trampolines laced on, was kept fully assembled, making breakdown and reassembly times short and simple, mostly because of not having to lace/unlace the tramps. Just the four bolts holding the amas, two clamps on the forward cabin top, and two tiedowns for the aft beam. When unattached, the frame assembly was turned 90 degrees and sat on top of the main hull for road transport.

Cheers,

 

it works

Just back and will pop up some more info later but we had a great little scoot about.

Cold as anything - took the ice off the car but in the sun it was lovely. Very little else on the water but even though we were alomst on high tide we kept grounding out the daggerboard and rudder, we willl need to move elsewhere for better testing.

We can get out into the sea but need to ensure we can get back in the nightmare channel entrance so we also tested the little trolling motor. Plan is to head out at the end o low tide in the deep channel, tool around in the sea and then ride the current back in but do need to be careful as seen quite a few boats bin it when they lose control in the channel.

An RS200 a while lost sail power and the eddies span them round and drove the open transom straight into the water and it immediately sank. The guy sailing it gave a comedy wave and shrug as it went down and he got dragged out by the lifeboat.

Anyway, today was absolutely brilliant and we've got a good idea of the changes needed in ride height, tiller extension position, changes needed for allowing cleating off sheets etc.

I moved the float back 50cm and will remove the last 50cm and seal off the final bulkhead taking the legth of the float to 4.25m compared to the main hull 4.75m.

Yes the plan is for the frame and floats to stay together, but at the moment we need to take it apart as transporting it backwards and forwards while making changes.

Can't wait get a few changes and strengthening done and get out and thrash it. Got straight up to just over 20kph so about 11 knots? in very little wind, with no tension in the sail in the crapped out old sails as well.

Wanted to ensure we remained underpowered while we got a feel for things.

Will get some more pics up shortly and also got some video that will need some editing.

Be interested in seeing people thoughts of it underway.