Does this unusually open interior layout have enough deck support?

The question was posed regarding the layout of #189, Tangaroa V. The full set of responses is included here firstly because of the very clear and evidence-based response at the end from Marius Corbin that is both a ‘yes, it is OK’, and gives insight into the structural design of the Corbin 39. Secondly it is interesting to compare that with some of the other responses, and to reflect on that when reading through and assessing the validity of some other opinions expressed elsewhere on other subjects.

a. Nice woodworking but a bit scary on the structural engineering, I’d say. Jack

b. Hi, we agree that these photos indicate a lack of deck support. Looks beautiful but waves on windows could be extra dangerous for this boat. Rod Kerry (#092, Vision Quest)

c. Are you saying that without more rigidity the hull might flex, allowing the windows to pop out? Maybe the pilothouse windows also? Skippers, A few days ago I sent you an email regarding a Corbin that was built without the main bulkhead under the pilothouse windows. I was concerned about structural integrity. Thus far, I have received only three responses. I feel it is incumbent upon us as the Corbin 39 Owners’ Group to comment on this departure from the original design plans. Is the present owner in danger of a serious accident? What about the person who buys this boat some time in the future? Please send your replies directly to me and I will post all of them on our Q and A page. I would like to hear from Marius Corbin and Collin Harty, especially. Lester

d. I find the photos of the open plan Corbin rather intriguing. The layout has definite similarities to the Nonsuch 30….also the Niagara 35 Encore Edition. …Jeremy

e. I would think the structural integrity of the deck would depend on where this person placed all the bulkheads. The cabin roof would sit on this particular bulkhead and I have not personally seen another Corbin where this main bulkhead was not there. I would be interested in hearing what Marius Corbin has to say since this was his design. Thanks, Christine Lawton.

f. While the boat may look very nice on the inside (as well as outside), there is no way i would ever raise a sail. The apparent absence of the structural bulkhead between the pilothouse and main saloon is a serious issue. i would suspect that stress transferred from the rigging (even just at dock or anchor with wakes and wind loads) will cause the deck to flex because of the missing bulkhead. Doug Archibald (s/v #158, Chaos !!) [The upper and intermediate chain plates are opposite the mast which is located at the aft head bulkhead. Therefore, the deck should not flex. Lester]

g. I’m surprised at the lack of comments / responses as there are many very knowledgeable owners here. Not being a naval architect or structurally inclined for that matter, I elected to decline a formal comment, but having had another look at the pics., I did not see the mast support ??? or is it keel stepped ?? anyway, without the bulkhead under the P.H., I would be reluctant to go ” off shore ” but for coastal cruising…..??.. I’m not qualified to comment. It looks like a very nice boat otherwise, Frank Bryant (s/v #186, Visitant) [Tangaroa has a substantial compression post under the mast which goes down to the hull. Lester]

h. Thanks for including me in this email and for posting #189, Tangaroa’s photos on your Corbin site. As our harbour-master, I appreciate your questioning and validating of this very uncommon Corbin design. This boat was designed and built in the second half of 1988 in Corbin’s yard and was also completely equipped in their yard including auto pilot, generator, air conditioning, etc. It had in mast furling, electric windlass,.etc. I have all the original drawings and documentation from Corbin including some comments by Mr. M. Corbin to the attention of the original owner. The interior was designed for a couple to live aboard in complete comfort with a very large living area and only one closed cabin, (forward) . Two heads are installed, one amidship on the port side and the other aft also on the port side . The whole volume under the cockpit is the engine room where the generator with its own diesel tank, water maker, main engine, (Perkins 60 HP), water pump are installed. Access to all those equipment is very good through cockpit deck that becomes a large hatch.The first owners took Tangaroa V down the Pacific Islands for a year or so and came back to Canada afterward. My intentions are to make Tangaroa V and its crew of two seaworthy for bluewater cruising. We expect to retire in about three year and start cruising wherever the winds take us. Best regards, Guy Viger (#189, Tangaroa V)

i. I have considerable boating experience but no professional qualifications. From the photos…I see a pair of semi bulkheads each side under the sill at the leading edge of the pilothouse where it joins the deck. These I assume are installed to the hull and below the floors as Corbin would have done. As the Corbin is cored and overbuilt this should be adequate support in this area, although I would add a couple of nicely finished posts from floor to deck head each side of the ladder joined to a shallow cross beam. The C & C’s of old used a system like that to open up the interior. I am concerned that the large area of the deck above the main cabin has no semi bulkheads or beams. I feel that in time this might lead to some deck flexing. The mast loads are carried to the keel by a compression post which is not visible The bulkhead (in the photo) in that area looks substantial. The cabinet work and upholstery are beautifully finished. The sofas and cabinets opposite are probably integrally glassed to the hull providing adequate support. Without more detail, especially measurements from the sill /leading edge of the pilothouse to the mast area support/bulkhead/compression post it is difficult to guess how much deck is unsupported. It appears that the main cabin forward bulkhead has been moved aft, locating it in the area of the mast? I believe I read in the original builders ads that one of these boats had been rigged and sailed with no interior at all except for a compression post ! It will be interesting to hear what the professionals have to say ! I am reminded of my Navy days sailing a 40 foot open wood gaff rigged cutter with just thwarts for side compression loads and stringers to prevent hogging and sagging. If all the cabinet work in Tangaroa is well glassed in to support the hull shape, then the deck just becomes a cover to keep out the weather. It is substantially constructed….has good camber…..but it does need reasonable support…..how much structural strength the deck adds to the whole boat is open to question ! Anyhow that’s my ten cents worth…and TangaroaV is one of the nicest Corbins I have seen ! Regards, Jeremy

j. The photos show a very nicely finished boat, both exterior and interior. As you note, the layout is very unusual. The instructions I received from Marius Corbin regarding the bulkheads was that there were 6 structural bulkheads and that they should be located not greater than + or – one foot from where the Dufour design showed them. I would think that the absence of a bulkhead where the front of the wheelhouse meets the deck cutout would result in a significant weakness. In Photo1 I can’t see any reinforcing such as a deck beam and there is no vertical pillar either. Regards, David Salter

k. I’ll have to fall back onto the sage wisdom of the anonymous broker who said “Corbins are like a box of chocolates, you never know what you’re going to get until you bite into one.” [This is true of every boat. Lester] It is simply impossible to say whether the interior layout of Tangaroa V has compromised her structural integrity by looking at the photos posted. It would take a much closer inspection of the boat to know. With structural PVC foams, knitted glass and/or carbon fibre, epoxy resins and substantially engineered structural knees, the technology exists to stiffen the hell out of a design like this. I would also note from the photos you posted that there seems to be a major bulkhead inline with the mast and major rigging loads. You would have to know more about the specifications of the sail plan, pull the headliner, delve deep into the lockers, and talk directly to the builder about his laminate schedules to know it this boat was engineered to take the necessary loads. There are a number of very high-end raised saloon and pilothouse boats on the market today that have opted for this very same open layout. It is possible to do, put impossible to know if it was done right solely by looking at these photos. Best regards, Collin Harty

l. Guy, Does Tangaroa have a compression post to the floor (not the sole) which supports the mast? (Answer: Yes, a 6″ diameter steel post) If yes, is there a bulkhead from the post to the hull, which braces this post? (Answer: Yes) Lester

m. As I mentioned to you, Tangaroa V has been cruised extensively in the South Pacific during more than one year. She is now almost 17 years old. There are no stress indication, (cracking, ….etc), anywhere on deck or below desk. I have attached more photographs that show the structural bulkheads on both the port and starboard side. As you can see they do not cover the whole area and thus allow the open view concept. This design conveys a tremendous feeling of space and volume that I have only seen in much bigger boats and is a great invitation to live aboard for extended periods of time. See Tangaroa Pics, Guy Viger.

n. Regarding the present layout, perhaps a structural header that spans from stbd to port hull ribs can carry the loads anticipated on an ocean crossing? I think it would be super if Marius Corbin could weigh-in on any kind of reductions in the bulkheads. [See A48n, below] I’m not speaking about total removal, but opening up the wall area on the port side just beyond the galley or the settee for example. Thank you kindly on your efforts in establishing the website. Tim O’Neil (#138, Whaleback- homeport Boston)

o. The Corbin was designed to be an ocean-going vessel. The plan provided for numerous bulkheads to give the boat the interior support for strength. This vessel looks to be missing 3 bulkheads that our boat has in the salon and pilothouse. I believe that this compromises the structure and could lead to possible problems such as hull flexing such as you describe. The deck is not getting the proper support and I cannot see a mast compression post in the salon. [It is in the aft inboard corner of the head compartment bulkhead. Lester] I personally would find this dangerous. Rod

p. Tangaroa, was one of the last layouts I designed and was factory built. Not to worry about the integrity of the design as far as strength is concerned. All the bulkheads are there and the boat is plenty strong. You seemed concerned about the one at the pilothouse. It is there, like all our bulkheads, laminated on both sides in the hull and in the deck. The part that seems to be missing, is the dash that unites the bulkhead to the windshield of the pilothouse. That part has never been structural and the bulkhead never went as high as the overhead of the pilothouse. That boat [Tangaroa V] is a 39′ like all the others. Tangaroa felt a lot bigger inside than the others, because of the openness of the design and two of that version [Demontigny] were built. I must confess that this is the layout I prefer for myself, maybe because it is the latest of all the layouts. Have a great day. Marius Corbin

q. Guy, 1. I know what the bolt heads are; they are rivet-like fasteners holding the pilothouse down onto the deck. On my Corbin, bolts were used and the nuts on the inside are covered by 1/2″ foam and 1/16″ vinyl sheeting. Also, your pilothouse appears to have a lid which is riveted on. It appears a separate mold was made in order to accommodate the two large hatches and the dorade holes in the roof. 2. The longest unsupported span, fore and aft, is 7′ on my Corbin. On most Corbins, it is about 10′. But on your boat, it is about 16′, from the companionway to the mast compression post. I think this is too long and a potential hazard in a heavy sea with a knockdown. 3. If I were you, before taking off around the world, I would consult a competent naval architect to look into this question. I recommend John Letcher, a PhD from Cal Tech, experienced singlehander, author of the first comprehensive study of self-steering techniques, designer of sailboats, and now a designer of boats and ships using computer techniques. He is located in Boothbay, Maine. 4. In order to be a bluewater boat, I think that TangaroaV needs a substantial beam athwartship where the forward end of the pilothouse sits on the deck. A SS truss about 6″ high would do the job and would fit into the open appearance of the interior. This beam could be tied to the existing wooden knees outboard and supported by two posts (lattice truss or poles) resting on the inboard ends of the two existing partial bulkheads, one in front of the helm and one between the back-to-back settees. That’s my two cents worth. Lester Helmus

r. Guy, Here are some further thoughts on this question One is redeeming, the other is less so. 1. In the severest of wind and sea conditions, Tangaroa should remain intact; the worst that might happen is loosened windshields, delaminated plywood, and/or delaminated fiberglass, all due to flexing of the unsupported main deck in the area of the windshields. Therefore, I conclude the Tangaroa open layout design is structurally safe. 2. When you go to stock up on victuals for that round-the-world cruise you are going to wish for the storage shelves and drawers that the main dashboard/bulkhead can provide. My #010, Insouciance has an additional bulkhead with shelves, drawers, and icebox-turned-storage box which is at the forward edge of the galley. This bulkhead plus a post lend added support to the deck which is needed for a keel-stepped mast. Good luck, Lester.

s. Our Corbin 39 hull #144, “Cormorant” was built by Don Ney in consultation with Marius Corbin. There is no bulkhead under the pilot house windows as in the factory models. This boat has been around the world one and half times and is still structurally sound. The inside steering station is mounted on a shoulder- high console (same level as deck) and is about 2.5 feet aft of the base of the forward pilot house windows (sort of a cathedral ceiling for the galley and main salon which really opens up the living space.) Don Ney told me that Marius Corbin toured the boat after he (Don) finished it and said “Why didn’t I think of that!” All the best, Harry and Jane Hungate, cruising in New Zealand in #144, Cormorant.