Saturday, May 18, 2013

Better Boarding--Extended Transoms

rev. 6-3-2013

On my last boat I had a few grand projects in mind that I delayed too long. They would have been fun. Extended length and beam, extended rig. On a Stiletto they wouldn't have been big money and they would have been exciting. I dithered too long.

I really like my PDQ 32. It may be the last boat I own. It certainly has the basic durability, I have determined that I am unlikely to cruise beyond the Chesapeake, and if I do ZTC has proven that is no problem. I like the smaller size as everything is lighter, and my joints aren't getting any better. I like the ease of getting slips.

So what would I fix, if I had a dream list?
  • AC. I hate the Cruise-n-Carry, but for now it will do. I will build something in when it breaks.
  • New mainsail. Mine has a terrible leach. Easy, I'll order a new one in a season or 2.
  • Pitching. Longer is better.
  • Easier boarding for my wife and parents. She has a fake knee, balance issues, and the nastiest ankle fracture I've ever seen, right through the joint surfaces. The cartilage in my right knee is also fading fast and I've been told further surgeries won't help. I wear a big knee brace a lot. My parents, of course, are quite long in the tooth but always game to go sailing.

And that's that whole list. I'm OK with the outboards. I like the kitchen and I like my propane heat just fine (we did a long cruise on 25-40F temperatures this winter and it did very well). I love the aft cabins and I love the 270 degree view from the salon. I like the size; bigger would mean bigger anchors, bigger sails, more maintenance, and higher sheeting loads. Not useful in a small place like the Chesapeake Bay. I like the small size for the smallest of harbors.


I am considering low transom extensions (like PDQ 36 Pacifica) rather than the high-sided extensions seen on the Seawind 1000/1000XLs; though the Seawind aesthetic is very nice, blocking the sugar scoop steps is incompatible with disabled access. There are a few faults in the Pacifica-style  extensions (did not follow hull lines but swooped up too quickly for best efficiency, and the profile was not faired to blend with the existing  topside lines) I can resolve and I really only need an 18-inch extension (note: became 22 inches as-built) to solve the boarding problem. They will be relatively low, like Pacifica's because I do not want the higher sides as on the Seawind extensions; we use the lower steps when boarding from floating docks. The high sides would flow nicely going up wind, but down wind they could catch waves, so while they look pretty, I believe they are less functional for us. Other benefits?
 After extension
  • Better speed? I doubt it will be measurable, and calculations suggest it will only matter at lower speeds. perhaps 0.1-0.3 knots, depending on the speed.
  • Load carrying. A little.
  • Pitch reduction. Won't hurt, but too small to notice.
  • Many days on-site fabricating. I live 1 hour away. Ugh.
  • Difficulty match gelcoat and fairing. Fortunately the bottom paint and boot top will cover most of them.
  • Increased resale value if done well. Of course, I may be dead by then.
  • Length. My slip is not priced per foot (fixed by beam) and the practical docking length does not change (transom will not extend beyond tender on davits). 
  • Appearance. I think I actually like the new lines a little better. certainly not ugly, if I spend some time playing with the curves and angles, matching her existing lines.
  • Fun. A place to dangle feet.
  • Practical. A place to wash pots.

As for building a mold, I'm considering simply applying several coats of PVA mold release to the last 30 inches of the hull and pulling a molds of the lower foot (all that I need). Yes, I would need to narrow the mold by taking a seam down the bottom. I would need to attach the form to plywood stations and glassed-in stringers, but I would get a nice smooth surface with the desired compound curvature; after all, I want to match the existing rate of curvature. This should save a LOT of fairing and any glaring transitions in hull form. Glassing in the platform and new transom is simple. There is no internal access so I'll have to include some sort of inspection ports; I'm sure they'll leak.

(Note: this is what I actually did.)
Alternatively, I may just build a metal mold, following the hull lines straight back. I've done this before; after getting the shape you like you fix it with transom and some stringers.

Very handy for boarding.

Your thoughts? Comments PLEASE. Forget structural concerns; I'm an engineer and will get past those. I think it will look OK and the function in terms of fun and practical access to the water, and limited mobility access to docks and the tender seem overwhelming.


Some practical considerations. I'll be collecting my notes here over the next few months.

No core in bottom half. The PDQ was laid up solid below the water line, and given the sidewalls are mostly below, I'm going to skip core materials. Just cloth and mat.

Epoxy resin. While polyester resin could certainly be used, I'm much more familiar with West Systems and there will be quite a bit of secondary bonding. It also smells better and I'll be working in the basement a lot. It is more water resistant and barrier coating will not be needed.

Pre-laminated FRP transoms. I have the scrap. Also tabbing and stringers, as needed.

(used pre-lam 1/4-inch FRP from McMaster/Carr)
Deck may be glassed 1/2-inch marine ply, unless I get a better idea. My FRP scrap is not wide enough.

(Yup, worked fine)
Tenting. I do not have an angle grinder with an effective vacuum attachment, so I may use an old camping tent. With the door open, it should swallow the work area.

The mold will most likely be 2-part to ease removal. I'm going to have to seam it down the center anyway....

As an alternative to pulling a mold from the hull I may build a sheet metal, simply strapping it to the hull, as was done by Roy Chandler in "A 30-foot, $6,000 Catamaran." He modified a stiletto27 by adding 3 feet to the transom, following the lead of the factory, which extended the hull to 30 feet using the same lines for the Stiletto 30. However, this would make it a bit trickier to beef up the form and I would like to keep the slight compound curvature.

rev. 6-3-2013

I'm leaning more to metal mold. This would allow me to do both hulls at the same time, since the mold is simple. It would allow me to do the work in the field, which would solve fitting problems. The PDQ 32 has a nice extended hull flange that will make bonding on-site very strong and simple. The mold will consist of the aluminum with ~ 6 firring strip stringers screwed to the outside and a square false transom on the tail (the actual transom will be angled and prelaminated, and tabbed in later, after trimming the initial layup). A metal mold can be 1-part as it will flex on removal, allowing it to be pealed off even if there is some sticking.

I've been practicing with the PVA and like it far better than wax; easy release and washes right off... with sweat drips if not careful.

Video of Pacifica installation process. Different approach.

Video of flow before modifications.


  1. You might be able to get past the gelcoat matching issue via a judiciously designed and painted on "swoop" trim feature...


  2. Seems a tremendous amount of work and effort for washing pots and better boarding. I looked at some of these extensions (only online) and feel what a shame the original design doesn't meet the needs or "wants" of so many. As an engineer and from your own doubts as to whether it will effect any performance to a noticeable degree, why not try and design a well shaped and glassed platform that can be easily attached to the lower step. I imagine the thickness of a surfboard or so and if it can be canter levered enough off the step it should be purposeful enough and you'd only need one. JMHO, redesigning hull forms should be a last resort.

    1. Don't underestimate the importance I place on better boarding; if my boat is not useful to my loved ones, it is of no use at all.

      I well understand the concern about modifying the hull design. Generally these things are designed as a whole by a smart team. This is one reason any extension will be short as practical, not the 3- to 6-foot extensions often seen. On the other hand I've been sailing multihulls for 25 years, I've sailed on boats that have been extended, and often the original design was sub-optimum; they have a way of gaining weight. Additionally, boat design is affected by the area and type of use; who is to say exactly what the design would look like if I he had used my criteria, at this point in my life. Different, of that I am sure.

      Example: if the typical large catamaran is $250,000-$350,000 and purchased by people over 65 years old, why are all of the steps 10-14 inches tall instead of the standard 7 1/2 inches? I took a pole at a recent Boat show (Annapolis Sail) while sitting in the cockpit of a large cat (tall steps) with a dozen potential buyers; "How many either personally have a joint replacement or a spouse with a joint replacement?" 70% of the hands went up; the designer had no response.

      I've sketched-up a few platform designs, much as you've described, for exactly the reasons you've described. They are compelling reasons and I may well go that way. But it won't be because of fear of work, for I plan own this boat for another 15 years. It will only be because I cannot resolve design issues to my satisfaction.

      But PLEASE keep the comments coming. They really help build perspective.

    2. Maybe a pair of telescoping supports coming from inside the hull to hold a simpler designed platform. I guess you could design a complete platform that would telescope with some considerable work (I'll never assume your afraid ha) but I'm not at all familiar with the inside hull structure in that area.

    3. Access to the area behind the transoms is absolutely hideous, for all intents sealed. In fact, the only way to remove the boarding ladder bolts will be with a grinder. Backing plates and through bolts are not possible without installing a large access plate, though I can certainly fabricate strong mounting points by bonding pads.

  3. I'll add 2 more cents. Staring at the sketch brainstorming, what stands out is the very small space gained from the extension. No doubt, if constructed from rebuilding the hulls (you will have to do both),you will step with complete confidence on that "small" space. How about a pair of fabricated SS slides running vertical down the face of the last step (bonded, bolted etc.) which I believe would be into the water. Then mating slides could be somehow attached to a platform and the whole could be dropped into place. I imagine it would sit atop the bottom step and be supported and canter levered from the slides. I hope I explain well enough, I'm really a "hands on" kind of guy with a bit of Trade School that got me started. For what it's worth, if you do go ahead and reform the hulls I think your idea of using the forward part of the hull as a mold and center-line cutting to thin it down is an EXCELLENT idea!

  4. One more quick about cutting out that next step face above, to gain access to the nether regions and build a bullet proof extended overhang/platform and then patch up the step with gel-coat.

  5. Instead of the extension, how about a molded step or two that folds up and lays on the existing steps? Hinged at the bottom, it could be flipped down to provide boarding and then flipped up. If built right, it would not prevent use of the steps when folded up as well.

    s/v Eolian

  6. Do it because you can. it makes the boat look nicer instead of the stubby look. It adds functionality. It don't look like some afterthought add-on. If you were buying a boat like this and there were two identical except for the extensions, but the extended boat was 5 to $10,000 more, would you buy it?