questions and ideas for rob denney

For over 2 decades now I have enjoyed the design and build thoughts from Rob. On many occasions I have wanted to ask follow up questions but held back not wanting to sidetrack a thread. More recently he has asked for ideas for advancing boat building in Fiji, so I thought a combo thread might lead to a lively and beneficial discussion of design and build ideas. Like Rob I see no need to agree on everything as ideas can be modified, expanded, refined, and tossed out depending how we perceive things individually. It would be refreshing to have a thread where everyone felt comfortable tossing out ideas for us to mull over without getting sidetracked into prolonged arguments. So Rob, question no. 1: Years ago now you introduced the concept of hinging bow (and stern?) sections. Have you actually built any hinged bows to test the concept? If so, how did they work? Some 36 years ago when I first got the multi bug I surmised 2 meter long bow and stern sections but hinged over onto the center decks, whereas your hinge concept is on the inner hull side. I felt a 1 meter spacing between top hinge and bottom fastenings would be safe. What do you think?

 

I was wondering if Rob had come to a final conclusion on telescopic masts, seems a project fraught with complications but I live in a bridge locked city (Perth) so it would be interesting to know. Sliding Gunter is another option.

 

I think what the world needs, is a 30ft Proa that fits in a 20ft container

 

I spent many years around the Swan and can remember well coming down river with the stick down on the old S&S 34, then working flat out to get it all back up during the run through the harbour, then a leisurely overnight jaunt to Bunbury and back. Good old days, except one time we encountered a sea container about 30Nm out and 30Nm south of Mandurah in a 50' cray boat, pierced the bow and gave all of our gear a rinse. Plugged it with a tarp, put the doctor on the stern and limped into Mandurah.

 

one way to Jacknife it. Bow starting at 1:20

 

That is very clever. Would it help if the inner side of the ww hull is perfectly flat (albeit resulting in an asymmetric hull) ?

 

Thanks Cando. I'm flattered. Sorry for the slow response, there have been some computer and internet issues here in Fiji.
Hinging ends are a good solution to marina costs and trailer lengths, especially on boats with flat sides, bottoms or decks so thery can be flush mounted. The theoretical loads are easily calculated for a particular boat, by assuming the entire section is under water. The load is not ridiculous, but failure is not an option, so oversizing them makes sense.

I have built a lot of composite hinges, but not for bows since I have not had length constraints. If I did, I would use composite hinge pins made by pulling fibreglass or carbon tow through pvc tube. These would be 20-25mm diameter to spread the load and ensure they didn't break. The housing for the pins would be tow or uni wrapped around the pins and onto the hull. No fastenings to leak or corrode. Tow is much easier to use as the uni must enter and exit the wrap at the same angle to ensure the fibres stay in alignment. Instructions on doing this are in the Harryproa plans.

Probably build the full length hulls including both bulkheads with a saw width between them, plus rebates for the hinges and attachment. Also some pins or hill/hollows to ensure they are aligned after the cut. Make the cut, then fit the hinges.

The hold down mechanism can also be a carbon pin, tapered to ease insertion and to apply some force to prevent movement. A stainless rod and nut (see Jackknife) could also be used. Both require alignment and access to the end of the hull to fit it. If it is for marina use, I would use dyneema and a winch or block and tackle to avoid this. Plus a horn cleat to reduce the chance of accidental release. Probably 2 of them as a failsafe.

Vertical lifting costs buoyancy, gives a bigger lever arm for the hold down and does not need antifouling. Horizontal makes motoring folded difficult, but not a problem if it is done in or near the marina berth.

As with most things boat (and particularly proa) related, nothing is set in stone. I welcome comments and experience so we can improve the set up.

 

The nature of joining things hinged or demountable or sliding or adjustable is always complication.
In my time as a fibreglass laminator the only way I saw to make 2 parts join in any semblance of neatness and fit was to mould one part off the other. You can make the shape of the jointing flange self locating and I have not done it but I dare say you could route in a groove for an O ring seal.
Another locking mechanism you could fabricate with tow would be folding cams like a quick release bicycle hub.
2c

 

Definitely complicated, but worth the effort in some cases. Not just for bridges but for building in short sheds and for reducing windage/lowering cog in strong winds which will result in a significant gain in upwind performance in a blow. We built 2 x 3 piece telescoping masts for the cargo proa for these reasons. A steep learning curve, accentuated by using pultruded carbon strips instead of laminating the sections.

The main issues are the sliding fit and raising/lowering. There needs to be a slot in the bearings for the raising/lowering line and the bearings need to be aligned so the mast can be put together, neither of which is trivial. Nor is the sail attachment if the top section is smaller diameter than the lower one. There are ways round these, but they all have performance effects. Next time, I would make and insert the bearings before joining the 2 halves of the mast. Join the smallest dia section first and use it to align the bearings in the next section, then join that and repeat.

Steinar is building a 3 part telescoping wing rig (with a novel control mechanism) for his 8m test Harry, prior to a 25 metre version for his 20m cruiser. The first section is under way, is typically high quality. we are still discussing he detail of the bearings and the hoist/lowering. A big advantage of wings on telescoping masts is they do not require loads of cunningham/downhaul/luff tension. This means a much smaller hoisting line can be used, resulting in smaller gaps between the bearings and the mast for it to run in.
The current cargo proa solution is short string kites. These require a low load bearing mast 12m high to launch and retrieve the kite, and to stop it falling in the water if the wind drops. (video of testing at Cargo Proa - Fiji — Harryproa https://www.harryproa.com/blog/cargo-proa-building-blog). Because we already have the lower (8m) sections of the masts installed, we will use these to hoist up 4m lengths of lightweight tube (bamboo or fibreglass). ie a gunter. This is a far easier solution then telescoping, with many of the advantages, especially if the mast overlap can be aligned with the wind over the sails. For non racers and cost/time/space constrained builds, this would be what I would suggest.

We also built telescoping beams on Elementarry.(7.5m Harryproa) which worked very well, although alignment needed to be precise for smooth operation. We used pins to lock them in place. Again, they were more work than external sliding joins which are much easier to build, operate and maintain.

 

Absolutely. In that design, the inner side IS perfectly flat, up until the height of the Lee hull. Then, we can build a bit more room out over the cross beams, to make more Nav space.
I expect the resistance to windward drift would be reduced by the flat side too.

 

Mr Watson, could I ask you to expand on yr ideas above ?
ie ; what /where would this be used ?
expected optimal finished width ?
Masts ?
How many dollars to send a 20' container to europe ?
Or is this another trailersailer option ?

 

I like sliding Gunter rigs, the hardware is easy to configure, for cruising there are a lot of pluses. I did a canoe that way using a molded gooseneck sleeve for the yard that gave a streamlined junction and skipped a trip to a machine shop.

 

What is the upper limit of boat size to use sliding Gunter rigs on?

 

Historically quite large, reference Chappelle.

 

Not sure what "optimal finished width" means. If you mean launched/assembled dimensions, they can be varied by using telescoping arms, of course.

Container transport cost benefits are very dependant on circumstances.
Sydney to Los Angeles is about $7000, but compared two/three months at sea minimum, plus the travel hazards of the open Pacific, plus food, insurance, personal suffering, its pretty cheap.
Considering its even cheaper to go from Europe to the USA,
Add to that the benefit off season sheltered storage. There are quite a few examples of boats left in tropical ports or ice-bound ports in the hurricane season, damaged in the open or on moorings.
Even leaving boats in the open in a civilised dry storage, the damage from rain, dirt, birds, theft etc is considerable.

Then, there is owners time. The boat can be moved safely, economically in two months to the next holiday location, while the owner is working to pay for the holiday. If they have to spend nearly two weeks moving the boat to a faraway destination, that's a big chunk of holiday time gone. That's not even considering the trip back. If your faraway paradise is a five week annual affair, most of the time is gone.

"Or is this another trailersailer option ?"
You may have noticed in the first drawing, some wheels and an axle. It would be entirely possible to also include a breakdown trailer in the container, so if you sent the container to a faraway port, you could have it moved locally, by trailer to other places easily.

Resale options - a boat this size could be worth $80k. Two weeks cross continent travel to a new purchaser is a few thousand, compared to the time and cost of having to drive both ways to tow the boat back to a remote location. Container Melbourne to Perth is $3,000 - way better than 2 trips for the buyer with a trailer, petrol , accommodation, etc

Masts probably wouldn't exceed 20ft by much, and if you needed more sail area, a Gunter rig is quite feasible. The major benefit of a multihull is being able to be easily driven by smaller sails.

These were the main points of consideration for the concept.