A maximalist outboard cruiser, why not?

Power cats,

Yes I have read your excellent article several times. Every time I finish it, I decide I will only design and build catamarans in future. Then I wander down to my local harbor, Gig Harbor, and wonder where I would put it.

Then, sketching up a candidate, I measure the total surface area, a classic weight estimator for aircraft, and find the Cat has roughly twice, or more, surface area (not wetted surface) of the equivalent accommodation monohull.

Whilst the hull of a mono, especially the ones we are describing here, can be considered a box beam for structural purposes, a catamaran is a pair of box beams, joined by a cantilever bridge. This, in itself, speaks to me of weight. I know you do light boats, but perhaps this is because you use modern design techniques, competing against monohulls still anchored in the 19th century.

Yes a power catamaran, especially ones similar to your designs, could be an alternate in this case.

My (rather weak) arguments might be;

As the length increases for accomidation, the beam must increase proportionately, to avoid interference drag from the hulls. Suddenly the beam is excessive, creating an issue with marinas not geared to 'cats', in locks if encountered, and overland transport. Admittedly, the 260 sq ft living area mentioned earlier only needs cabin space about 21' long assuming a cabin beam of 12'.

Even a 12' cabin beam, given demountable hulls, is potentially an issue with land transport. Given a cabin beam of 8', to allow ease of transport, the cabin would now be 32' long, and how long would the new hulls be, even given a much wider floating beam.

Let's assume an 8' high cabin (your basic design) and a trailer designed to support the cabin very low to the road, we could stand a 13' wide cabin on its side. This implies a 20' long cabin, implying 40-45' long hulls. This might be a worthwhile exercise.

One of the benefits of having multiple engines, is the ability to use just one at economical RPM for cruising, whilst tilting the others out of the water. Catamarans are difficult to handle, and rather inefficient, with just one hull powered.

You mention the quality of increased speed per power of a catamaran. I'm not sure this is entirely true, power is usually derived from weight, with supporting rolls played by wave drag, and skin friction. Given the long skinny nature of these proposals, I suspect they will use a similar power to deliver similar performance, the skinny limit being stability. Admittedly, the cat form will deliver greater speed with less fuss given more power.

In regards to speed. I think it is the quality of the journey that matters, hence the wittering on about noise, or lack thereof, during the moving part of the journey. I want a relaxed, and if necessary slow passage, though the ability to cover miles quickly at a dramatically increased fuel cost might be a useful attribute.

 

Two articals in Wooden Boat Magazine #244, May 2015, are pertinent to this discussion. The first describes a 24' X 6.5' OB cruiser specifically intended for the 'loop'. It has one of my favorite hull shape solutions, the diagonal chine.

The second is a much larger 32' X 10' stitch and glue twin diesel.

Both have another great feature, a distinguishing 'knuckle' in the side, visually lowering the profile height somewhat.
The first could easily be linnialy scaled up to, say, 8' beam, though the cabin top should be kept at the same (current) height. It could also be stretched modestly too. Though I am personally not a fan, the stitch and glue process could also be used here too.

A curious note being the larger boat is stitched from 1/8" ply initially, with more layers of 1/8" ply added to meet the necessary scantlings. I personally have had little success laminating ply to ply, but there is nothing wrong with building thickness after the initial shape molding.

 

Construction

Some notes on construction.

My suggestion of using diagonal solid wood planks for the skin, making no attempt at making them watertight, then covering this with a thin plywood layer for waterproofing is basically a intermediate step between a thick structural skin, no stringers, or even frames, like a typical older fiberglass boat, and a hull with skin and stringers. In this case the stringers increase in size and structural contribution, whilst the skin proper reduces in thickness to the minimum. The diagonal form reduces the span of each structural member (vertical/transverse would be even better for this), whilst increasing torsional support, and allowing significant double curvature.

Any further thoughts on this method?

 

Materials and Methods of Hull Construction

Alan,
I'm not able to post intelligently about cellulose building systems as I'm a metal boat builder. If I want a light weight hull I rely on welded aluminum, not that it's the last word, but; it's what I know and have built in.

Most of my work has shown a very good strength to weight ratio in the (couple hundred) commercial fishing boats I've built so I've not spent time with wood and hardened goops as building materials. In our location and market, wooden boats just "can't cut the mustard" in regard hauling enough catch and lasting with those 5x and 10x (all up) hull mass loads.

If I were designing this project I'd work in welded aluminum even if the cost may be higher? but its a matter of my background not that this building system is the "end all" material.

Using an example 30' trailerable hull and either inboards or outboard power, I'd expect the wood to metal wt. as about 2:1 or 3:1 in most cases? Not sure on that (?) but that is what I've seen in the commercial fishing boat fleets I've worked in. So to me a lighter weight, longer hull that will be trailered seems like welded aluminum would be the most cost effective material choice due to the lower overall wt of the finished boat?

Cheers,
Kevin Morin
Kenai, AK

 

One problem I've been having in my efforts to date: V-Berths!

Long isn't a problem in a long, skinny boat ... wide OTOH.

And while I've found mention of suitable berth widths I've yet to run across anything about that notch between them: how wide at the minimum and how deep is desirable for easy access to a berth that may be the dimensions of a long, comfy couch with the back cushions taken out for extra shoulder room.

Especially if there's a bevy of weak knees and backs in your family with which any crawling in and out of bed must be accomplished.

Oh, and of course for my family: the need to be able to help put a handicapped sister in one.

 

I suggest you abandon V berths altogether, and put the head right forward, with the bowl centerline, facing forward. There is plenty of stowage space under a counter either side, and a shower could be worked in too. I find showering whilst sitting on the head itself quite practical, especially whilst underway, though my wife cannot stand this, demanding a 'proper' separate shower stall.

This layout, with the head right forward, and a pair of berths either side just aft separated by a bulkhead, was pretty standard in the long narrow "Lake Union Cruisers" of yesteryear. Aft of the above berths, usually with another bulkhead, was a galley, helm station, cane seats, and sometimes another pair of berths.

If you have an invalid, then you should attempt all measures for their comfort, as having them enjoy the trip will really pay dividends. I suggest an absolutely flat floor from transom to head, just above the waterline. I would consider making an open transom, flush with the floor, about 3' wide, with the OB's on the transom, on either quarter. This allows a wheelchair access at the stern, then to traverse the whole floor, stern to head. In fact, if you wish I can forward a design for the small wheelchair with 360' swivel we did for aircraft access.

I think Bolger did a couple of concepts like this.

 

For clarification, here are some images of 'Lake Union Cruisers".

 

Hi! Thanks.

Actually my needs are a bit different: it isn't mobility but taking care of business ... literally.

My sister has cerebral palsy and doesn't take care of her own poop ... or pee. So we need a can big enough for her and whoever is cleaning up, leaving space for them to work. "Them" is often "me" and I'm huge ... just my feet are 16EEEE. I also am no where near as flexible as I once was (but who is?).

So a can far forward under not much headroom may not be the bee's knees for my purposes (just as I like the idea of interior layouts with very few step up or down because of my Mom's weak knees).

In terms of layout I've been looking at a Bolger Wyoming inspired craft with a generous self draining aft cockpit on the same level or one step above the main cabin volume where most stuff will be ... a small raised pilot house off to a side opposite the chart desk with the V-berth a couple of steps down ahead of that with lower standing headroom.

At this point the head could either be partly under the dash with extra headroom and the pilot's chair set up higher still or in the main volume with the captain's chair pushed farther forward ... as Bolger did with the Wyoming. As with the Wyoming there would be a bow cockpit.

As a practical matter if I ever do get to build I'll probably have to build a full scale mock up of the bathroom. It may seem odd to cite Gilligan's Island but that raft simulator they had on the show might be just the thing.

 

You have your work cut out, but it is a worthy goal cruising in such a situation. I still think you could use a variant of the far forward head. Think in terms of a longer, and therefor wider head compartment, yet still in the bow. Consider larger holes in the forward bulkhead for assistants access, closed with auxiliary doors. The 'Lake Union Cruiser' often had a full headroom bow, under the raised forward deck, and this profile allows this. All things considered, this long narrow form, with outboards, is quite practical for the class of accommodation you need, lending itself to the continuous flat floor from stern to head. Raised boxes either side of the passageway make excellent bases for helm seats.

I agree the hard chine form allows the floor of a head compartment to extend out all the way out to the sides. This might allow a side head compartment in leu of a berth, wide but shallow. Unfortunately, now what does one do with the bow compartment. A "V" berth is not really an option under your circumstance, and apart from stowage, I'm plum out of ideas.

The "Lake Union Cruiser" profile could be excellent for this purpose, being long, lean, and efficient. Most such vessels have a hard (firm) rounded chine, I don't think I've seen otherwise. My favorite, in the family of a colleague, built when he was about 10 years old, used galvanized angle iron, about 2" X 2" I think, on 14" centers, bent into the hull frame shapes. This was covered by cedar planks, bolted to each frame with galvanized gutter bolts. No sealant, glue, or caulking, just expansion from immersion. After 60+ years around Seattle, admittedly usually in fresh water, and three engine changes, and replacing a few of the bolts with SS, the hull interior still has its original Linseed Oil coating.

 

I've something like a Lake Union Cruiser in my gallery that would be ... heavier and therefore even more expensive than an enlarged Wyoming.

Probably prettier though.

Really, I just need to win the lottery.

... or maybe just buy a ticket once.

 

It's always good to dream, it keeps us moving forward. To be honest, I WAS thinking of a Wyoming in all respects, but with the 'Lake Union Cruiser' as the profile. Apart from being even more 'wind rode' than usual, I cannot see any reason such a vessel would not be quite successful, and therefore quite a reasonable 'dream' ship, especially for your circumstances.

This vessel would probably also benefit from a long 'box' keel, ballast for sure, and a better keel for maneuvering, possibly even battery stowage. I believe there are some electric 40' versions of this on the Murry River in austrailia.

 

As a retired aircraft designer, I should favor aluminium construction too. However, a couple of bad experiences with supposedly marine grade alloys, on the Boeing boats, made me a bit cautious. I'm sure such issues are well and truly corected by now, but how does one ensure the correct alloy.

Yes, welded aluminium could be an excellent material for the boats we are describing here.

Good crack about the cellulose, but I might suggest a 'cellular' design, especially of the hull floor.

My questions would be: it seems noisey inside such a vessel, ie welded aluminium transmits and possibley amplifies sound (reverberation?), and how do we deal with this.

Metal skins, well highly conductive skins, exposed to differential temperatures 'sweat' resulting in condensation. We called it 'rain in the plane' and it was a bear to eradicate. How do you insulate, or otherwise treat the interior, whilst allowing the inside skin to be inspected for corrosion, damage, or repair?

 

Incidentally, I finally found a file of the patent (Canadian #563453) for Gilwood ... which was invented mid 50s. Gilwood is a plywood reinforced with wire mesh. I first came across it in an old Popular Mechanics here: https://books.google.com/books?id=n...CUQ6AEwAQ#v=onepage&q=gilwood plywood&f=false

The patent had no specific data to back up the P.M.'s article's claim of 10x stronger than 1/4" plywood but it did include data from a 9" ring test where they took a 3" plunger hitting material supported by a 9" ring. I.O.W. a test relevant to puncture. This was performed where he was apparently a professor, at Oregon State (then a college).

(The picture in the article shows a different test being performed)

The Gilwood tested used inferior plies compared to the stock plywood (and this was mid 50s plywood, which people now seem to claim was great compared to what we've got today but in the patent was not described as good based on the lumber available as had been). The 1/4", 3 ply plus one layer of 23.5 gauge 1/4" mesh was twice as resilient, at over 2000# thrust (and very little difference between specimens tested) than the 1/4" standard fare at its best (750#, down to 200# for one sample ... it varied a lot). It was around twice what 3/8" standard fare produced.

The strongest samples described in the patent was for 1/2", 5 ply DF, 1/16" outer plies, 1/8" inner, front ply grade B, back C, and 3 inner plies of the sort normally rejected for making plywood because of defects. It had two mesh layers vs one as before and managed 3,620 psi in the ring test.

I only have one file for our current high tech stuff: a paper that compared using 12K carbon fiber with less expensive 3K stuff and was focused on the effect of bending strength, not punch through, ands also failure of wood plies.

So no idea how good the Gilwood claims really are.

edit and DERP! I just now realized: the worst 1/4" specimen was 1/10th the strength of the Gilwood. ...

 

Finishing Welded Aluminum

Sailor Alan,
Material Test Reports (MTR's) are not very often demanded of aluminum suppliers even if the alloy failures a few years past has made all points of the supply chain more tuned to the need to provide a "chain of custody" record of the metallurgy's certification of legacy; there still may be suppliers unwilling to produce these critical documents? But if you offer a purchase contract with MTR's required in it; and refuse the shipment without them.... the issue of the purchased alloy being the specified alloy will go away.

I've sold highly engineered metal parts to Arctic Oil and Gas production companies (read world class name oil companies) where pipe fittings, of all types, require a couple dozen 'cert.'s for every single set of fittings. I've learned that in the real world, truly professional integrity requires Mine to Refiner to Mill to Extruder to Supplier (and finally) to User confirmation of the alloys.

It will take years for the PNW marine industry to become lax again; in regard alloy certification of their products. But oddly enough you have to make quite a bit of noise to get these documents form most suppliers.

In most metal finish designs a series of chemical boundaries are considered normal. First, a series of chemical bonds to the aluminum to allow oxide replacement (allodyne) to put a chromium oxide on to replace aluminum oxide so that paints, insulation's, and sound deadening (mounting) adhesives can be added without risk of future crevice corrosion at the underlying marine alloys.

[This has to happen in all steel boats as well, just a different set of oxide removal and replacement films in those boats.]

Once adequate oxide films and bonded prep layers are installed various plastic foams can be installed to provide heat, sound and vibration dampening. There are lead/foam/foil panel materials that will leave an engine box so quiet it simply hums. This is proven by the quieting gen'r'tr boxes (aluminum and "sono-lead" clam shells with generators in them) typically used in live a board's and Class A motor homes.

Like any refrigerated container (steel shipping containers) humidity is dealt with by air circulation and a dehumidifying element. (AC) So once this theoretical "trailerable", long range, narrow L/B ratio hull is conceived; using welded aluminum allows the living spaces to be coated to avoid corrosion, foamed to insulate and avoid 'raining' and.... the drive/gen set would be in a sono-lead paneled sealed enclosure with all air in, exhaust out, routed to accommodate sound, heat and side wall vibration.

I guess I'm asking: Why is it that virtually all the mega yachts from places like FedShip that have the AA Lloyd's rating.... are welded aluminum? How are these yachts silenced? How are they insulated? How are the world cruising, highest quality floating palaces solving these problems?

So, the S/W ratio is highest (of marine aluminum) and that allows the lightest all up displacement, then adding materials to the metal surfaces to do 'that' spaces' job heat retentive/reflective; sound retentive/attenuating, is just a matter of lining each space in the boat with the needed spec. material.

I see this project as most effectively designed using welded aluminum and the current generation of products used to insulate, sound attenuate, and accommodate the living surfaces and spaces.

I don't view a chromate primed (after etching) aluminum hull and cabin need any inspection if the chromate film is covered with adhesive and styrene plastic sheet material, then covered with wood veneer or plastic sheet materials. I've seen boats with this combination last for four decades and when I opened the wall panels the materials were pristine.

Cheers,
Kevin Morin
Kenai, AK

 

V bunks stink, tiny space and rotten motion.

Why not install the engine in the bow, with nthe head next to block engine room noise?

With todays fly weight engines ballance should not be a concern.

With a thrust bearing on the prop shaft , simple ((and cheap) truck drive shaft parts will span the distance .

Its been done on larger boats 50-55ft + and works superbly .

These had 3000lb + engine packages , today a working setup could easily be inder 1000lbs , and perhaps down to 600lbs with good selection.