Hobie Hulls (buyer's remorse)

Discussion in 'Multihulls' started by Owly, Feb 22, 2020.

  1. Owly
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    Owly Senior Member

    I did read the post, but decided to lift the deck. It took about half an hour after I had removed the pylons..... they practically fell out once I cut around them. The deck join came away very easily once I got started. I used an air chisel along the seam, gradually working in deeper as I went around several times. The bonding paste fractured almost effortlessly..... I had a laugh seeing the reckless abandon they resorted to with it........ It was slathered all over the bottom side of the deck for no apparent reason. It'll make it easy to fit bulkheads using a joggle stick setup. It would be nice if they were bonded to the outer skin. I was a bit shocked at the crappy core material, or actually at the bond or lack thereof. It's polyurethane foam as someone else said.... basically the same stuff they use for sticking flowers in for arrangements. Not bad building material if used properly. The extreme thin foam doesn't make sense on a hull side that takes a pounding in the water. There is a LOT of delamination in the hull sides that would not have happened if they had used a thicker core so it would resist flexing more. The bare hull without deck or pylons still weighs 42 lbs. The delam is a damn shame, as without the bond, the two skins work separately and essentially have no more strength than a single skin. Foam sandwich was a good idea to build a stiff hull without a lot of weight, but technology has come a long way since the days this was built! I'm rather curious as to how they bonded the core to the outer skin, because obviously it was done in a female mold. That joint is where the delamination failure seems to be... it's where the delamination failure is on yachts too.......... very expensive failures that have bankrupted a number of manufacturers over the years. David Pasco, a marine surveyor has a series of interesting articles on the subject..... Here is a link to just one of many;
    Marine Surveying : Composits - High Tech Materials in Boat Building https://yachtsurvey.com/HiTech.htm

    Now I have to figure out what I'm going to do with these hulls.... what the best course of action is. It shouldn't be difficult to make two 14 foot hulls stiff enough. I'm not sure I'm determined enough to simply cut away the internal glass and remove the core foam, and replace that with some light weight spruce stringers and a couple of bulkheads, but that seems the logical course. Breaking the hull up into 3 segments with the bulkheads, the stiffening needed would be pretty minimal. The deck is pretty soft too...
    As it stands, I don't have much........ The deck would not be difficult to replace...... I got it off without damage.

    H.W.
     
  2. Owly
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    Owly Senior Member

    I would consider this a bit of an extreme.... more labor than the hulls are worth........... The original however was not vacuum bagged but rather hand laid. There is a HUGE difference in resin usage when vacuum bagging....... I would not attempt this, but if done right it would be lighter....marine foams are rigid, so just getting the foam into the shape is a problem.... There just is not an easy solution that I can think of............
     
  3. Corley
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    Corley epoxy coated

    Well, how heavy it is comes down to your technique, careful application of a squeegee on the inner glass when you replace the core and it shouldn't be significantly heavier. The normal process is to do it in two wetouts first the layer between the outer hull shell and foam core is vacc bagged in place then second stage is the inner glass. Keep in mind the hull already has some weight in foam core and glass which you are simply replacing whilst addressing the delam issues between the outer skin and core. As I said above it's probably not worth the effort on old H16 hulls but is relatively common to do on larger hulls with core separation or core failure situations.
     
  4. trip the light fandango
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    trip the light fandango Senior Member

    That sounds like a successful couple of hours, my posts were seated by someone in a hurry who didn't expect them to be ever seen again, I couldn't knock them out with a heavy hammer, very solid, the deck join/flange is also really tough . To use the hulls you will need to pretty much replicate the flange that was cut off but on the inside and out using hardwood quad like a canoe, I'm guessing. It's easy to relaminate the skins if your careful without adding much weight. , you may as well halve the height of the hulls now to something closer to the volume/weight you actually need and leave the deck off. Apart from good old yank high falutin marketing[here we go] there's good reason they're the most successful cat ever, which includes longevity and robustness.
     
    Last edited: Feb 25, 2020
  5. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    There is not a huge difference between hand lay-up and vacuum bagging.
    Please don't spread such falsehoods on a public forum.
     
  6. Owly
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    Owly Senior Member

    I didn't cut anything off.. the flange is still completely intact, and I could if I wanted to simply bond the old deck back on. We're thinking along the same lines as far as gunnels and displacement... as far as relaminating the skins.... I'm thinking about simply removing the inner and installing some light weight spruce stringers. I'll have two bulkheads spaced about 6' apart that will support the beams, that leaves about 4' forward and 4' aft, dividing the boat into 3 logical sections that could easily support themselves with a few stringers........ approaching a skin on frame boat ;-) Removal of the useless inner skin...... structurally useless as the core is not bonded to one of the skins, and removal of the thin core, which weighs almost nothing should be quite easy. My inclination would be to remove these locally initially to fit the bulkheads, and leave as much of the structure intact as possible as long as possible to help retain the shape. The stringers would be located, and bonded to the hull sides with epoxy cabosil, using screws through from the outside for clamping, later removed and the holes filled with the same and sanded smooth.
    As far as displacement, I would like enough to step on without nearly submerging it..... a good number including the weight of the hull itself is probably around 300 - 350 lbs.... about 5.35 cubic feet or 40 gallons of water. I should be able to rough figure that treating each cross section as a triangle, figuring the area of a typical triangular section, and extrapolating / interpolating / estimating. The actual total displacement to deck is what I'm talking about, and that isn't a published figure. As it sits, I suspect it would not have enough structural strength to hold it's shape with 40 gallons of water in it, which would be the easy way. The other hull still has the deck and pylons, I could perhaps cut out the pylons and make a large central access to remove the flotation foam, then pour in 40 gallons of water with the hull leveled up, then reach in and mark the level.
    I'm thinking that aside from some ply deck either side of the bulkheads that support the beams, and a bit at the transom and bow, the remainder of the deck could be doped aircraft fabric to keep weight down as much as possible.

    Your idea of "really tough" and mine apparently are not quite the same....... it took very little time for me to break the adhesive holding the deck on and pry it loose. Granted I used an air chisel to walk down the crack once I got it started. Once I had fractured the adhesive at the edge of the flange all the way around, it was easy to get the fracture to run all the way to the inside, and separate the two. The bow and stern were troublesome. The adhesive is brittle stuff..... essentially not a lot different from polyester autobody filler.

    This an interesting project, and may not prove as much of a challenge as I was thinking......... I'll do a lot of that before proceeding (thinking). I'm starting with nothing for all intents and purposes, and building a boat in reverse... from the outside in.

    If I knew anybody who wanted a set of pylons, it would be nice to find them a home...... they are perfect, and from what I've read, they are a problem area. They have large chunks of deck attached to which they are well bonded, so could easily be refitted into someone else's hulls. I also have all the beams, but two of the fittings for were cracked by the time I got them off the pylons with a dead blow hammer. None of it has any value to me except as scrap aluminum.

    H.W.
     
  7. Owly
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    Owly Senior Member

    My quick and dirty calculations show that the Hobie 14b hulls at their stock dimensions should displace very close to what I want. This was done by taking triangle measurements in 3 places equidistant in the hulls, working out the areas, averaging them, and multiplying by the distance. I was working at about 100" total out of 14', and just using a WAG about the bow and stern, where the dimensions contract more rapidly. I found center, which was the widest point, and measured off 50" each direction, taking straight line triangle measurements inside to the bottom and across. The result was 27 gallons. This does not take into account the positive curvature or hull thickness, but my wild *** guess puts me over the 40 gallon mark including bow and stern, but not a lot....... close enough for government work ;-) I'm saying between 350 and 400 lbs total submerged displacement.
    The internet makes the need to use fancy geometric formulas obsolete......... just google "triangle calculator", and enter the numbers...........

    P.S. A bit off topic, but I do not actually use Google anymore...... Duck Duck Go doesn't track you are deluge you with advertising or give people who pay first ranking in search results........ I'm not looking back. Goodbye Google!

    H.W.
     
  8. trip the light fandango
    Joined: Apr 2018
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    trip the light fandango Senior Member

    Removal of the "useless" thin skin, I question this logic, I know you have significant delamination but it is easy to re attach skins to foam, drill through and reattach with plugs made of resin and flock in the weak spots[or inject a q cell slurry into the skin that is loose, or sikoflex polyurethane] like where you stood on them,...oops ,sorry. if you pull the gun whales in tighter the surface tension will take up some of the slack. I did misunderstand how you removed the deck, you have about 1/3 of the strength left now. Fill up the other hull with water[or bind the open one with rope] with the blocks left in , because the hulls are asymmetric I think your estimate will be under, it will be easy to add the foam block dimensions. Build quality is very different on the hulls I have seen, the blokes signed off on my hulls, maybe they were paid properly over here or had a good boss, either way they took some pride in their work. If you remove the sandwich foam the hulls will go limp. Why would you put decks on the hulls when weight is your biggest issue, just strap in the foam, aren't you using them for one season? Duck duck go sounds interesting.
     
    Last edited: Feb 25, 2020
  9. guzzis3
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    guzzis3 Senior Member

    I've only skimmed the post. Do you know how old the hobie is you bought ? The early ones were built like tanks.

    They are probably the worst choice possible for outriggers. Heavy, heavily rockered and low bouyancy. They are called off the beach cats for a reason. They were built to launch through surf and to be surfed like a surfboard. They are built to survive pitchpoling. Later designs were made to race in flat open water. Higher volume, less wetted area less rocker, even boats which relied on the hulls to go to windward.

    You would be better off getting gary dierkings book and building some ply or foam cored floats. GD's book is superb. I actually get it out and reread it about once a year.
     
    Manfred.pech and fallguy like this.
  10. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Been a ddg user for awhile now. Got sick of google selling me after purchasing...and probably getting credit for it somehow as well.

    If you made a mostly solid cylinder of xps foam of 10" diameter, I get about 50 gallons; if you installed 1/4" plywood at 10" wide by 14" long; the center ply would be 9 pounds, and using foamular 250 is 1.55 pounds/cuft; you'd add 12 pounds; add 5 pounds for glue and you are at a whopping 26 pounds. Cover the surface with 6 oz glass and epoxy or 12 oz per sqyd at 4 yards, call it 5 and you are at another 4 pounds, say 5 with some fairing or 32 pounds rounding up.

    You could also avoid glassing them just in case you were not sure about performance.

    The heaviest part is the ply and that could be eliminated with some 1708 as well.
     
  11. Manfred.pech
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    Manfred.pech Senior Member

    Yes, I agree. Hobie Alter was looking for a design to go through the surf which means not too much buoyancy especially in the ends and no boards. He found the catamaran design of Woody Brown, copied it and developed the 14 ft and shortly after the bigger one. It was a great success. But later on the designs changed to the
    normal cat designs with bigger hulls with more static and hydrodynamic lift.
    Dick Newick adopted the hobie 16 hulls for his tremolino and wrote that the hulls make better floats for a tri than hulls for a cat. Later on he designed his own floats for the shiverer (tremolino). The boat was faster and was tracking a lot better.
    Hobie hulls are very very cheap now and they seem to be a bargain to the hobby boatbuilder. But they are heavy and not easy to join to the main hull. The flat outer sides offer some lift to windward but the asymmetric inner sides only work at a certain angle of attack and laminar ? flow. Bouyancy is low for the weight as is the hydrodynamic lift. The lift to drag (form drag and skin friction) ratio is not favourable. For the sons of my youngest son I have built my own floats with ply and polystyrene on the bottom for a good shape (weight 10kg each at 11ft) and they work well.
     
    Last edited: Feb 28, 2020
  12. Owly
    Joined: Oct 2016
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    Owly Senior Member

    Lots of ideas here.............. "buyers remorse" was the title for a reason ;-( I have no idea as the age of these.... probably very old. No serial number tags anywhere I can find on either hulls or tramp frame. They have a lot of rocker, and that's OK for an ama I think. I plan to mount them such that I can change their depth compared to the main hull fairly easily, so that they just barely skim in still water at rest level.... or whatever seems to work best for me, but also can be submerged more when anchored camping out.

    Interestingly the hull I have not removed the deck from is quite solid, lacking the extensive delamination of the other one...... go figure!! No I did not stomp on the hull creating the delamination as has been implied.... I pushed on it using my foot to check stiffness, and the first hull gave easily showing existing softness / extensive delamination, and just that light pressure resulted in the clear sound of foam separating from skin. Most of the upper portion on one side is very soft on that hull showing that is largely delaminated, the forward portion on the outboard side being the worst. The deck also exhibits a lot of delam on that float. It's as if they are from two different boats.

    There clearly are better options as many have described here........ I have a model I made some time back of a float designed to be built from ply using stitch and glue, and use ply efficiently. Getting max displacement for minimum material, the idea being to make them 12' long.

    I don't consider that I have "lost" anything considering the value the rudders and associated hardware have to me, along with the various clutches and other hardware that will be useful, and the fact that I already have ideas for using the longitudinal aluminum extrusions from the tramp in another project. The arched fore and aft ones have no value to me.
    I'm still leaning toward building a boat from the outside in so to speak. Using joggle sticks to fit the 2 bulkheads, stripping the inner glass and foam where they go, so I can tab them to the outer skin only, and building them with cutouts for stringers..... it would not take many stringers to gain enough stiffness. The lower portion of the hull is mostly sound or appears to be. I see no reason to leave the useless separated core and inner skin, but perhaps some of the cored hull can be used. Terminating the remaining cored section properly might be an interesting challenge, but removing some of the core and working some thickened epoxy into the void to fill it like putty to seal out any moisture would probably work. Clean the remaining surface as much as practical and blow out the dust, then a cake decorator's bag with epoxy / cabosil, followed by a rounded shaping tool to remove any surplus. With some luck, perhaps only one hull will need to be treated this way. I really do not see any simple and cost effective way to repair the extensive delamination on the one hull. The solutions proposed do not appeal to me such as creating posts joining the two skins, or vacuum bagging new core and skin, which I feel would not really work without a mold of some kind to hold shape during the process. Stringers are a cheap and simple solution, and I feel will work fine as I have to install bulkheads anyway, so the spans are fairly short. A third central bulkhead would help to hold shape and 1/4 ply is fairly light. There is no reason for the bulkheads to be solid. My inclination at the moment is to dive into it, saving what I can, and repairing what I must using inexpensive fir lumber for stringers, and ordinary 1/4" CDX for bulkheads, sealing it the best I can with thinned epoxy (20% denatured alcohol).

    The plan is to only use these hulls for one season.........tentatively, but I know how hard "roundtuits" are to come by, and experience shows that things I only intended to use briefly end up being used far longer than expected.............. I suspect we all have this problem ;-)

    I have a basic plan at this point, and it ignores some of the excellent suggestions made here........but that's the way things always end up. When I come back lamenting the failure of my plan, everybody can say "I told you so".

    H.W.
     
  13. upchurchmr
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    upchurchmr Senior Member

    Nice to see some good discussion.

    I lost my "round-tuit" in Japan and regret it. My wife gave it to me for obvious reasons.

    It would be interesting to see what you plan. There wouldn't be any "second guessing" on my part.

    I also never take all the good suggestions. :D
     
  14. Owly
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    Owly Senior Member

    Ultimately the final decision is up to me...... as are the consequences of that choice. One can waffle, mired in indecision faced with lots of great ideas, and never move forward. I'm not a young man, and I have a lifetime of successes and failures to draw on, I never lose sight of the fact that everything ultimately falls on me. I often joke "do something even if it's wrong".... and in my business I actually practice it........ Collect as much information and as many ideas as possible, make the decision with your eyes wide open, accept the consequences....... correct as needed. My customers appreciate that........... I get the job done. It may not be perfect initially, and they understand that as we are usually operating in terra incognito........But I will do what is necessary to make it work long term......... Most folks are unwilling to make difficult decisions..... I'm not.... but I don't go there without doing the groundwork, tapping what resources are available. You put yourself in a position of responsibility, and move forward. Mistakes will be made no matter how much groundwork you do, but doing nothing is not an option..........The same businesses call me again and again, so I must be doing something right ;-) After 40 years of this stuff, I have no fear of making mistakes , though I do my best to avoid them.

    I had a good chuckle about the wife and the "round-tuit".............. I understand all about honey do lists and such, though I got off that train many years ago.........

    H.W.
     

  15. Owly
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    Owly Senior Member

    I have both hulls sitting side by side in cradles contoured for them and designed to hold them parallel. Both are have the decks removed. My tentative plan at this point is to install a couple of bulkheads in each hull, stripping away the inner shell and foam at each location, and tabbing them solidly onto the outer shell using epoxy cabosil, and fiberglass tape. These will be the structural bulkheads that support the beams. I may also install a central bulkhead. These will be of 1/4" fir marine ply. Once this is done, I will remove the rest of the inner shell and foam core, and install external doug fir stringers, as I see no real reason they need to be inside except aesthetics. Nicely rounded corners, and fairly low profile, and finished with a small bead of epoxy cabosil at the intersection and painted with the hulls they won't look bad. They will be glued to the hulls, with thickened epoxy, with screws from the inside for clamping..... later removed and the holes filled. This eliminates the problems of trying to install stringers and bulkheads inside. I'm seriously considering doing the stringers as the first step, before the bulkheads, and screwing through the entire structure....... Needless to say the gelcoat will be removed before gluing. A larger gunnel strip will be added also. The deck will be mostly doped heat shrunk dacron aircraft fabric, with ply in strategic places such as adjoining the load bearing bulkheads, and where access openings are desirable.
    This project has morphed into a thinking project......... what am I going to do, and how am I going to do it. I find myself running through the sequence of events again and again to find flaws in the procedure before I encounter them in real life. This is the way I tend to do things...........Build them in my mind hundreds of times before building them in real life. I've done many complex projects this way with good success.......... It took me awhile to come round to the external stringers, but in the context of what I'm doing, it makes sense. Function takes precedence. I'm hoping to keep weight down to around 35 lbs each.... less than half the original weight, but that may be optimistic. The Hobie hulls were built for abuse that these won't see, in fact I seriously considered skin on frame construction, which was how I built my first ever boat back in '67. A few years later I graduated to cedar strip........

    H.W.
     
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