Building Logs

Close your gaping hull hole

Posted by Paul

The rudders are hung, so now I am working on the outboard doors, the last thing I want to complete before I lower the boat back down. Only because I will be bolting these parts in through the hull so having them a little higher makes access just a touch easier. Next job after this is to mount the outboard tracks which will be much easier once the boat is level again. And of course, I am still waiting on the outboard slider bearings (yes, I know, I have no-one to blame but myself. 5 months and counting on this job. The rudder bearings took 3 months, I figured about the same on the outboard rudders. I keep getting the same answer. Real busy, will get to your job next, give us a couple of days, so I wait 2 weeks before returning to the same answer). So hopefully by they will be ready just when I need them next week. Who else believes that?

starboard rudder tiller and hydraulic ram

As mentioned in the last post, we (Terry, Ray and I) drilled the rudder post holes to take the bolts to hold the tiller in place. We had to constantly re-sharpen the drill bit, solid carbon really kills them. We drilled half way from each side and the holes lined up very well. The bottom bolt on each shaft slides in and out really easily but the top one a bit stiffer even after multiple reaming with the drill. But upon mounting in the boat, the top one slid in and out really easily and the bottom one binds a little. Life! I then re-dry fitted the hydraulic rams to see how the final set up lines up. The gap between the tiller and the ram is about 40mm, I set it at this gap so that the bolt that joins them has enough gap to have 2 nuts (one to tighten to the tiller one to tighten to the ram) and still a bit of a gap so they can be tightened or loosened independent of each other.

The keen eyed among you will note that there doesnt seem to be enough clearance for the ram shaft on the other lock and that the hull side looks to be in the way by about 30mm. I think that is the case but wont know for sure until I connect it all up. It may just make it. If not I have a simple solution, cut a hole in the hull side for the ram to go through and build a cap on it on the other side.

To recap on what I am doing now and why. I need to make doors that open up into the outboard well, that seal the hull shape when sailing (and the outboard is raised) and open to allow the outboard leg to drop through the bottom of the hull for motoring. The doors need to open inwards only, so that they can never disrupt the water flow under the hull. No disrespect meant to the designers but their method of doing this, whilst extremely simple is full of other problems. Their solution (my fall back position should I not be able to resolve my issues) is to have an aluminium plate attached to the skeg of the outboard that pulls up to the under hull when the outboard is raised closing off the hole, but trails under the outboard when motoring like a para-vane which creates a lot of drag by sucking the sterns down, and some have been known to be torn off by that drag load, not to mention the drag effecting either fuel efficiency or speed or both (and the range on a set amount of fuel).

Other designers that have outboards use a pod alongside each hull under the bridgedeck (sometimes called a nacelle) to hang the outboard so that it lowers to the water using its own (hydraulic) tilting mechanism and this is perhaps the most simple solution but the disadvantages are that it creates a place that waves can slam against and that it places the outboards closer together which inhibits slightly the manoeuvrability and it is also better to have the props directly in front of the rudders (another issue might be security, the outboards are out of the boat and visible as opposed to inside a lockable area and invisible). So the idea of coming down through the hull, whilst full of its own technical issues is a good idea overall, especially if I can successfully solve the technical problems associated with the design. The various pro’s and con’s of each design (outboard deployment methods) highlight the ever constant notion that every decision is a series of compromises.

Anyway, regardless of my preferences my boat has the outboards in the hulls so I have to resolve the issues so that I make the most of the benefits and minimise the negatives. And the big negative I want to try to avoid are the problems associated with having a plate hung below the outboard causing drag. I am resigned to losing one of the major benefits of the skeg plate design, simply because replicating it without the skeg plate might be too complicated for me to resolve. The benefit I speak of is the ability to have a single action mechanism. With a skeg plate the hole is sealed by the base plate attached to the outboard and is automatically sealed when the outboard reaches the top of its travel, in fact the plate would be the stopper of the travel. And of course the moment you lower the outboard the doorway is opened by the plate lowering with the rest of the outboard. Single action. In order to replicate a single action without a skeg plate I need to figure out how to make the doors open before the outboard starts travelling when lowered and to close after the bottom tip of the outboard skeg has cleared the inside of the hull (so not necessarily at the top of its travel but very close to as there isnt much clearance left). And to complicate matters further, the outboard travels about 400mm  from the up position to the down but the doors only travel in a 90 degree arc of about 100mm from open to closed. Single action is going to be difficult to engineer into this space. I might have to resign myself to 2 actions, open the doors-lower the outboard, raise the outboard – close the doors. If anyone has any ideas on how to engineer this simply please let me know. I have gone over a million ideas in my head but cant seem to nail one that I think both works and is easy to set up and wont be prone to breakdown.

But before any of that engineering can take place I first needed to make the doors. So with the rudders hung I set that as my next task. And it occured to me that because the hull is curved slightly, hinging the doors is going to be a little more difficult. The area looks flat but it is ever so slightly curved, and a hinge door can only work if the hinges are exactly in line along a flat straight plane, an curve puts the hinges out of sync. So the solution will be to mount the hinges on tables elevated off the doors slightly so as to bring them back onto the same plane. And this is something too difficult to do inside a narrow well. Solution; do it on a work bench first.

I already have the openings cut into the hulls and the buoyancy chambers built into the bottom of the wells leaving the column the outboard leg will travel through starting about 100mm above the waterline all the way to the inside skin of the hull and glassed to the outside skin leaving a thick solid glass flange about 4mm  thick. That flange is about 50mm fore and aft and about 20mm each side. Onto that flange I plan to attach a plate that will have the doors made into it. That plate I will construct in the well itself using it as a mold, then remove it from the boat, clean it up and cut the doors into it and hinge them, adding the hinge table to bring them back into alignment. Then re-install it into the boat and bolt it in. It will be removable should any repairs or modifications be needed at some later time. So first step was to create the mold in the well itself. I cleaned up any raised areas and rough spots in the glassing and covered the entire area in packaging tape. I also made up a plate from plywood to close the hole from below, covered it with the same tape and wedged it up against the hull from below using jacks. The base of ply had to be flexible enough that I could jack it up and around the rocker present in the hull at the stern. Over the length of the outboard well (700mm) it is about 7mm so a 1:100 incline. But the panel also had to be rigid enough that it would provide a solid base to the mold so as to retain the shape while the glass set. Using car jacks I wedged it up against the hull bottom.

rocker of hull at outboard well

The result being a full mold that the glass would not stick to in order to make the glass door plate and have it fit the well exactly and finish flush with the outside hull surface.

starboard outboard well taped to make mold starboard outboard well mold base ready to raise into place starboard outboard well door mold from inside

For many years I have favoured wetting out glass on a plastic sheet on a bench and carry it wet to the job and applying. I figure its easier to work standing at a bench and I also figure that I get a better glass to resin ratio and more even spread. I use the trusty old scraper to spread the resin over the glass. I had to resin 12 sheets of glass into the outboard well to make the door panel and I started out wetting sheets on the table as usual but after a couple of layers switched to laying a dry sheet of glass and brushing resin on, in other words wetting out on the job, which is a very common way of glassing. Most probably favour wetting out on the job. It was so much easier to wet these sheets out “in situ”, it must have saved me an hour and a dozen climbs up and down the stairs. And the brush ensured the glass was well pushed down into the corners and coves and that there were no voids. A combination of brush and consolidating roller will see this glass well compacted down into a very solid and strong panel from which I can cut the doors out and the remaining ring will remain strong.

starboard outboard well door panel glassed

Once set I used a jack to slowly push the panel up into the boat and off its mold base. Once free I removed all tape from the mold and any that had stuck to the plate and removed (with a grinder) the rough overhanging glass and generally cleaned the panel up and dropped it back into the opening from above and it fell onto the flanges perfectly. You can see in the pic below that it has a defined edge that protrudes into the hull skin opening and flanges that sit against the inside hull skin. The protruding shape exactly matches the opening so that the thinnest of lines presents along the waterflow and the bottom of the protruding plate is exactly flush with the hull and in the exact shape (rocker) as seen in the pic below.

starboard door panel upside down showing rocker

starboard outboard well panel showing mounting flange starboard outboard panel back in place after clean up

With one side successfully done the next step is to make the other, and then to cut the doors into the panels, make the hinge tables and attach them and hinge the doors and anti-foul them re-insert the finished panels back into the hulls and fasten them in (about 8 small bolts and silicone sealant) and the doors are done, now to figure out how to open and close them in unison with the outboard motors. Like I said, all advise gratefully accepted.

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4 thoughts on “Close your gaping hull hole

  1. SteveB

    I hope you manage to get your dream on the water soon. I have been following your blog for a long time, and must admire you for your perseverance. However this is the first time I have thought to comment.

    Have you considered the enormous forces that will be in play with the doors closed in rough weather? I don’t know how to calculate the answer, but can you imagine the stern slamming down hard, and the strength needed to handle that impact. Or a breaking wave coming from behind. Those boards will need to take a lot of the pressure from the churning water that pushes the stern of the boat up.

    I can see a risk of fittings being ripped out, and who knows wehat might happen then.

    Also, presumably the boards will not provide a watertight seal so the compartment will gradually fill with water to the waterline (anyway, it will already be full from when the outboard was used). This additional weight will severely impact the buoyancy at the stern.

    Maybe you have these issues covered, but I did not see that. Can you just leave the wells open and focus on improving the water flow?

    Disclaimer. I know nothing about building boats, but I do have similar sized cruising cat.


  2. Greg Smith

    Good work Paul. The problem of sealing the outboard wells has confounded me also, as the plans aren’t great on their solution. I was thinking of a pivoting arrangement so that the flange at the base of the outboards could move around a pivoting point, rather than be fixed which would cause the drag you mentioned. I would prefer another solution. I’m thinking something like the James Bond Aston Martin where the flap opens and out come a machine gun or whatever. Possibly a mechanically operated sliding door which could give a good seal, but again, two operations, and in a hostile wet well. You’ve got me thinking and researching other options.
    Bye the way, Kerry and I will be at SCIBS in two weeks, and will pass on any useful tips we see.
    Best wishes,

  3. Paul

    Hi Greg, Sorry for the delay in replying, for some reason all comments went to spam, and I did not get the usual email notification and just happened to be doing some back end house keeping and noticed your post.

    I initially thought about a bread box/desk top type roll top door made from plastic strips cut from a plastic chopping board with an aluminium rail each side with a gentle curve and you could easily have this push-pull with the outboard raise-lower, as it goes up it pulls the cord that pulls the door shut and visa versa, very simple and easy. My concern with the idea was the risk of jamming especialy if a crustacean managed to get itself into the rail. But I still think this idea has some merit.

  4. Paul

    Hi Steve.

    I am not so concerned about pressures exerted when slamming in heavy weather. I agree there will be some force but I dont think it will rip the doors off, rather push them open somewhat and perhaps I may need to build into whatever mechanism I settle on to keep them closed, some kind of shock absorption to handle those loads. Rigid things tend to break somewhere, whereas things that have some give, give under load then return to normal.

    I have for a while wondered whether they really do need to be closed and I may experiment with that once launched. That is, leave the doors open (the doors open inward so wont be in the waterflow under the hull) with the motors up and see what if any, the turbulence and or drag caused by being open is created. I have friends that race Endeavour monos that have outboard “columns” that deploy the prop in front of the rudder in a similar way. They have just a board with spring steel above it that pushes against the sides of the column when racing with the motor pulled up out of the column and stored inside the boat usually just on a bunk. That plate is just sitting in place and rarely if ever is moved. Granted, they arent racing in tough conditions, never the less, Endeavours are a 30 year old design and the outboard column has never been an issue with the design. And many of them race with the plate not replaced so it does not seem to matter, open or closed. (I know, because we forgot to replace the plate many times and we could not detect any impediment!).

    And you are quite correct, the water will remain in the column, I will not be waterproofing or sealing the doors, if I did so I would need to insert pumps to pump the water out. The water carried will be about 20 litres in each hull, so 20kgs. I am not too concerned about that much weight. It is the reason the columns were build into the wells, to limit the amount of water that would be carried. It would be even less had I decided upon small outboards (9.9hp) from the get go, because I originally intended to fit 25hp Evinrude Etec’s (and will one day when finances improve) I needed to build the columns deep enough fore to aft to accommodate the larger cav plates these motors have that the 9.9’s do not. The boxes built in the well that create the columns are sealed and act as reserve buoyancy that will make up for the weight of the column of water.

    In the end, this is all guess work. My fall back position is to just follow the designers design and fit plates to the outboard skegs that closes the hole from below. This is open to me at anytime and is easy to retro fit, albeit I would need to beach her or pull her out, but could easily fit them between tides on a dry out beach. And in the end is my get out jail card. If all else fails, this is where we will end up. I want to if I can avoid having to drag that skeg plate around every time I motor. We will see if its possible. It may not be.

    There is one other Schionning cat that employs a similar method so as to avoid the skeg plate. I think its called Plum Loco out of Coffs Harbour. I think he a single door and uses a dowel to push the door down then lowers the outboard down onto them to hold it closed. I am trying to make it just a little more user friendly.

    Thanks for reading and your comments. Hopefully, like most other problems I confront, a solution will present itself.

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