Multihull Structure Thoughts

[skaraborgcraft]

Not a Hirondelle 20, but a "cracksman"

Cracksman 20 - Wikipedia

en.wikipedia.org

 

[oldmulti]

Skarabougcraft. The Hirondelle 20 and "Cracksman" sold very well at the time. The Hirondelle was extended and subsequently widen in later production versions. The Chacksman had a bigger cabin put on but both cats suffered the same problem. They were good cats but the cost of building them increased to the point where they were uneconomic to produce at an affordable price. People were prepared to pay twice the price for a cat EG 4 foot longer cat with more space or performance, but a solid smaller cruising catamaran needs to be as cheap as a Hobie 20 or I will choose the Hobie 20 type thinking.

Reality there is a market for a smaller cruising catamaran but only at a price people can afford, and our society is dividing into a few people with a lot of money and many with a little money and many expenses.

 

[HelmutSheina]

Back in 2019 we published a small catamaran design by Mark Grumpecht. Mark built the design in a year himself but I could not find any plans for the design. The cat was later sold and no further details came forth. A small request and hopefully someone can lead us to the plans of this cat. I do not know if Mark is still active or someone has a copy of the plans. If they do, could they please advise us as the design looked good.

Mark Grumpecht small cruising catamaran is 22 x 8.5 foot weighing 1900 lbs with 24 foot wing mast as used on his Drifter 17 trimaran design. The cat has a lifting centreboard and central rudder. Mark designed and built the cat in one year. It is plywood with light e-glass cloth outside. It uses mahogany wood on the interior and for some framing etc. I do not know any structural dimensions. The cat has aft sugar scoops with steps.

The cat is trailable on a 3500 lbs capable trailer (the trailer weighs 700 lbs). The engine is a 6 HP long shaft outboard. The custom mast raising rig, uses trailer winch. The cat has two single speed winches mounted on the cabin top. The cockpit is 5.5 x 6.5 foot and the cat has a micro galley with a 2 burner propane cook top and small sink. The cat has a custom private head with door on port side and a thetford porcelain marine head. The cat has a double berth with 2 child single berths. The front mini tramp can have 1 adult or 2 children on it is very comfy and cool to be on while sailing or at anchor. The cat is a coastal cruiser that is claimed to perform well.

The jpegs give the idea but we need more detail please.

OM, Mark Gumprecht did a 17' Drifter Tri also that had a small cabin, and I cannot find any plans for it. i sent an email to an address he had on plans for a smaller Tri and heard nothing back, but old emails die too.

Building the Drifter 17 Trimaran – Interview with Mark Gumprecht

The Drifter 17 trimaran is a fabulous-looking craft built by Mark Gumprecht. Having previously designed, built & sailed smaller tris, Mark has spent recent months building this beauty, which features both cockpit and small cuddy cabin for camp-cruising. And it's all set upon a platform with a...

smalltrimaran.co.uk

 

[brian eiland]

Both the world’s largest sailing multihull (58m) and what is rumoured to be the largest ‘proper’ sailing monohull (as opposed to sail-assisted) at around 120m, are in fit-out today and will sport DynaRigs. First seen on Maltese Falcon 25 years ago, these freestanding masts rotate so the yard arms and soft sails can be set to suit the wind angle.

Southern Spars the proven DynaRig is the answer for certain sizes and applications, especially with the 3 latest projects it has in production. In cost and practical terms, it makes much sense – for vessels over a certain size (around 65m+ LOA) and for passage making, it is hard to match.

I was also much inspired by the dynarig development as it was introduced on MF.
This was my interpretation on a catamaran,..
DynaRig MotorSailer https://www.runningtideyachts.com/dynarig/

 

[brian eiland]

 

[jamez]

Hi folks,
While rummaging through some old files I found the following which I think I got from a member called Oldsailor (hope your still out there mate) many moons ago. Anyway I know some of you are interested in the older 1960-70s trimaran designs. There are a bunch in this document which looks to be compiled from a number of old plans catalogues. Enjoy.

 

[HelmutSheina]

Hi folks,
While rummaging through some old files I found the following which I think I got from a member called Oldsailor (hope your still out there mate) many moons ago. Anyway I know some of you are interested in the older 1960-70s trimaran designs. There are a bunch in this document which looks to be compiled from a number of old plans catalogues. Enjoy.

Thanks for this, there is even a couple of tris by some Skip Johnson bloke who just happened to like your post.

 

[Skip Johnson]

Thanks for this, there is even a couple of tris by some Skip Johnson bloke who just happened to like your post.

Ah but not that Skip Johnson ;-)

 

[oldmulti]

Thanks Jamez. Pat McGrath (who ran Canadian multihull services and produced the original doco for the PDF above) married an Australian lady and moved to Australia 40 plus year ago. Pat was a very knowledgeable person (who "invented" BoteCote epoxy) and a lot of fun. When having a meal with Pat and Lock Crowther you learnt a lot. The designs in the PDF were the best and/or the most popular at the time. Multihull designs have moved on since these boats, but the basics were starting to show through. EG Skip Johnson, Jim Brown and Lock Crowthers trimarans each had excellent concepts that with modern float design would work very well today. The real difference is in the building materials. Foam glass flat panels in SOME countries can be a cheaper faster build than plywood. Ah the good old days.

 

[SolGato]

I think Skip was onto something with the Seawing 24, his first production molded boat.

Mine was the last to be made and a bit of a hot rod with carbon used in newer designed floats and in the longer aero shaped beam arms which increased the beam width allowing for a bigger rig.

If my boat is any indication of his continued efforts to refine the design which I understand he may have started on as early as the mid 80’s, then I have no doubt it would have continued to evolve while taking full advantage of modern materials, techniques and design philosophies.

With a little less rocker, a bit more girth in the floats (they have good volume but are tall and slim) and a carbon rig and synthetic rigging, a Seawing 24 would really fly, but I’m not complaining…

 

[brian eiland]

this was a hot sailing trimaran,...a Firefly 26 tri.
I did not design the original Dragonfly which I tried to import, but rather set down and improved the design when I could no longer get product.

It was a sweet sailing boat. RunningTideYachts, Ltd. - Archives https://www.runningtideyachts.com/archives/Firefly.php

Trimaran Design

details of the redesign,.....

1) We lengthened the main hull by a foot to provide more buoyancy in the stern and cut some small drag experienced there; (the original boat subsequently did the same).


2) We eliminated the transom-hung rudder and designed an entirely new kick-up system to fit into a newly created slot in the stern extension. This allowed the hull to act as an end plate for the top of the rudder blade.


3) The amas were lengthened by 2.5 feet both to provide additional buoyancy in their tails when hard on the wind, and to allow for the aft crossbeam (aka) to be moved from bi-secting the cockpit, to a new location at the aft bulkhead of the cockpit; (this cockpit obstacle was one of the greatest concerns of potential buyers).


4) The aluminum crossbeams were changed from elliptical section tubes that passed thru fiberglass openings in the main hull, to round circular tubes where the AKA tubes would slide thru concentric tubes bonded into the main hull. This produced a stronger structure, and one that was less demanding of the owner in setting-up the boat properly. An added bonus was realized when we were able to hinge & hang the amas from the protracted extensions of the main hull's receptacle tubes during trailering, and during set-up and disassembly; (the original design required two people to detach the amas entirely and place them on a rack for trailering


5) The mainsheet traveler was moved from bisecting the cockpit, to a position atop the aft cockpit railing, and formed into a circular track which follows the new loose-footed mainsail.


6) The rig was totally redesigned in form and function. The sailplan area itself was increased in size and redistributed to balance the new retractable centerboard arrangement. The mainsail was a new shape, and its traditional boom at the bottom was eliminated. Correspondingly the sheeting angle of the mainsheet had to be correlated with the circular traveler track arrangement in combination with the absence of the normal outhaul force provided by a boom.


Often overlooked was the correct rotation function of the rotating mast. It is to be preferred that the mast rotate on its own into full rotation, rather than having to be manually induced into position. Then all that's necessary is a simple rotation limiter that automatically stops and sets the mast at a preset rotation limit upon tacking. This was all accomplished by careful attention to 3 factors, separate, and in combination; a) the location of the center of rotation chosen for the mast's cross-section (determined by the design of the casting at the base of the mast), b) the design of the hound fixture with respect to the separate attachments of the shrouds and the forestay, and c) considerations given to the fact that a boomless mainsheet arrangement acts to pull the mast back out of rotation.


An entirely new mast extrusion shape was selected along with a 2-ft taller spar. This new shape was superior aerodynamically, as well as lighter in weight for handling during trailerable rigging.


The lower shroud attachment points were changed from a single location at the ama deck lip to an upside-down ‘Y' arrangement with two points of attachment at the outer ends of the AKA beams (spread the load, and provided an athwartship mast stabilizer system during the raising and lowering operation).


7) A kick-up, pivoting centerboard was designed to replace the original daggerboard and trunk. It was unconventionally placed off the true centerline of the boat, and incorporated in a rectangular box that became a structural backbone of the boat. The off-center location was chosen to limit damage to the leading edge of the centerboard upon beaching & to keep gravel and sand out of the trunk. Eliminating the huge daggerboard trunk really opened up the relatively small interior of this boat.

There were numerous other detail changes that were made, and a number of others in the planing stages. Wherever possible we retained the same looks of the original boat as it had always received admiring compliments, and we had invested a lot of marketing time and money already. We really felt that our new Firefly 26 had the potential to become the J-24 of multihulls, particularly with an initial strong marketing program through our 50+ beach catamaran dealers at the time (ref our archive letter to those dealers). The F-27 trailerable trimaran program was developing concurrently, and we felt their massive print advertising campaign could only help us as well; plus! we had a distribution/dealer program in place that they were not considering at that time.


Unfortunately this was all not to be. Several financial hiccups and finally a partnership disillusionment killed the project. We had built six boats including the prototype. And they were all fun to sail!!

 

[SolGato]

this was a hot sailing trimaran,...a Firefly 26 tri.
I did not design the original Dragonfly which I tried to import, but rather set down and improved the design when I could no longer get product.

It was a sweet sailing boat. RunningTideYachts, Ltd. - Archives https://www.runningtideyachts.com/archives/Firefly.php
View attachment 209572

Trimaran Design

details of the redesign,.....


There were numerous other detail changes that were made, and a number of others in the planing stages. Wherever possible we retained the same looks of the original boat as it had always received admiring compliments, and we had invested a lot of marketing time and money already. We really felt that our new Firefly 26 had the potential to become the J-24 of multihulls, particularly with an initial strong marketing program through our 50+ beach catamaran dealers at the time (ref our archive letter to those dealers). The F-27 trailerable trimaran program was developing concurrently, and we felt their massive print advertising campaign could only help us as well; plus! we had a distribution/dealer program in place that they were not considering at that time.


Unfortunately this was all not to be. Several financial hiccups and finally a partnership disillusionment killed the project. We had built six boats including the prototype. And they were all fun to sail!!

Do you know how many of your boats are still out there being sailed and how they have held up?

I think I remember seeing one for sale years ago.

Your comment about mast rotation is interesting as I just finished fabricating a new “limiter” for mine since my mast has no problem rotating to 90 on it own.

How did the beam tubes attach to the floats? Sockets or clamps?

What did you estimate the float weights to be?

 

[brian eiland]

tubes attached via bolts that bolted to backing plates that fit into deck-to-hull ribs of the float hulls

don't remember those weights of the float hulls. i do recall that one of my first sub-contracted builder took it upon himself to not follow my layup specs, and built some overweight floats,....i fired them right away.

 

[oldmulti]

A short story that gives the idea of how to build a cheap boat. Be warned you will still take the same amount of time to build the cat or tri, it will be cheaper to build but you will have more maintenance and very likely have a much lower resale value or you will be giving the boat away.

There was a Californian guy who had smaller day cats but eventually he wanted a bigger boat to widen his horizon a little. He noticed a large number of plain plywood boats working the fishing trade off Northern California. Some of them were more than ten years old and still looked strong. So, he built the larger Wharram cat. He used exterior plywood, plastic resin glue, galvanized nails, and plain alkyd enamel on the hulls. The decks were covered with a mixture of linseed oil, pine tar, and turpentine. Inside, the hulls were treated with just linseed oil. He declared her ready for sea after one year of construction. With family aboard the cat made a trouble-free voyage across the Pacific to Hawaii. From there they sailed northeast to catch the westerlies and had a downwind slide to Alaska. After a leisurely gunkhole cruise south they stopped for a while in Seattle.

When I asked about maintenance, he said it was constant. But he called it mindless, dum-dum maintenance; two coffee cans with the deck mixture, and two kids each with a rag. In one afternoon with the kids working the deck, he could paint another coat of enamel on the hulls. That would last about eight months. Kauamea has her bilges painted up to the waterline with epoxy resin. This is in each hull from bow to stern. The same protection could have been had cheaper using a polyester resin. Cheaper still I could have used roofing tar. All the metal hardware on Kauamea is 6mm 316 low-carbon stainless steel. He wondered how 6 mm mild steel, heated, dipped in oil, then painted with Rustoleum would have worked. Expensive is good, cheap is bad are the watchwords today. But down at Fisherman Terminal there are a lot of empty Sears Weather beater paint cans. And those long voyaging heroes of ours seem to have done their sailing in good cheap boats. Today there are great varieties of adhesives and coatings in the roofing industry. The recreation vehicle and trailer industry has many good things the boat owner can use, and cheaper.

The family has since sailed further south and as far as I know they are sailing still. The point is maybe we are being spoiled by the plastic industry to where we close our eyes on other methods.

Below gives you and idea of Wharram cats in the 38 to 63 foot range. There is a Tehini 51 footer that sailed for many years had steel H beams as their cross beams. There were many other Wharram’s out there with second hand monohull rigs and sails and quite a few that have Junk rigs (not recommended by Wharram). It is possible to build a cheap boat but please remember another approach is to build a 30 footer in good materials instead of a 45 footer in cheap materials. The 30 footer will often be cheaper and on the water sooner.

 

[tane]

when building my Wharram (34' Tangaroa Mk I) in the late 70s I tried to navigate the shoals of cheap-&-maintenance-intensive vs. too-expensive-for-me-as- teacher-in-his-early-20s: cheap Finnish plywood & Austrian lumber, galvanised screws, Resorcinol glues, Epoxi & PU paint, aluminium mast & Hong Kong sails,...of course it was sold considerably under construction costs 7 years later (was still a worthwhile undertaking though, because it took us rtw. Adventures not possible anymore in this day & age).
With the secondhand market today & the costs of materials, home-building is an indulgence & not a financially driven endeavour any more (I am currently building a 22' monohull in ply/Epoxi - it will end up as expensive as a serial built boat, but the aim right now is in the building, not any more in "getting-to-the-South-Seas-at-my-low-budget"