Building a Marco Polo Tender

[Geoff C]

For the past few years we have kept our one-design sailboat and our Sea Skiff on separate moorings, and have therefore needed a rowboat to get to and from. I hit on the idea of building a 12' skiff (the length limit at the dinghy dock) in the garage during the winter, cartopping it up to Maine, and selling it at the end of the season. This is the skiff I built, treading the fine line between being nice enough that I'm not embarrassed to be seen in it, and not so nice that someone would want to run off with it.


Actually, we kept the oars in it at the dock, and many times people borrowed it and brought it back, so I'm a little less nervous about the theft issue. My plan to sell it so I wouldn't have to haul it home worked as planned. I sold it after two seasons of use for several times what the materials cost.

Which brings us to this year, and the need to replace the skiff. I've always been partial to L. Francis Herreshoff's Tender for the Marco Polo, plans for which are in Sensible Cruising Designs.


It's a sail and row pram, designed to be built dory style, measuring 11 1/2' long and 4 1/2' wide, with a standing lug rig and leeboards. Compared to the skiff it will have more stability, more carrying capacity, and we can take the grandkids sailing in it. Should make a great family boat.

For those wondering if I am going to build it in the original, heavy style of construction, the answer is no. My Statement of Requirements is different than those of the original, and the first priority is that it must be light enough to cartop. I know that when it is done, I'm not going to wish it was a pound heavier, and less material used is less material paid for. Speaking of paid for, I already have three sheets of 6mm okoume ply that should be perfect for my needs.

The first order of business is to enlarge the plans. I took the book to Staples and had them blown up, way up. To 4' x 6 1/2' to be precise.



At this size, the details at the top of the sheet, such as the tiller, mast thwart, rowing seat, and mid-ship frame, are at actual size. This will make it easy to transfer the details to wood.

For those of you who followed my previous sailing canoe thread, http://forum.woodenboat.com/showthre...anoe&highlight , the following few steps will seem familiar.

The first step I've taken is to make a model in Greg Carlson's Hulls program.



This enables me to quickly check the panel layout on the plywood, to see where it all will fit.



Fits on three sheets? Check.


On to the Freeship model......

[Ian McColgin]

Have fun. I've rowed one and was most impressed. Super both light and laden. Keep us aboard.

[Thad Van Gilder]

Its on my bucket list of boats to build.... ply bottom and cedar sides are my plan.

[Ian McColgin]

This is one boat where a bit of weight won't harm. I'd build ply all over, epoxy glued and CPES'd, and then, expecting some rough landings, I'd put a sacrificial plank bottom over.

If one were to use an outboard, I'd really beef up the transoms, shear strake, gunnels, and hooks so she could work well as a butt boat towing and pushing.

[CundysHarbor]

These boats are a lot of fun; I built one in the seventies for use as a tender. She rows well, carries a ton of gear, is safe for young children and tows well. Mine was per the Herreshoff design although plywood would be good also. Since the sections are all similar (all the angles between strakes are the same) you can bandsaw each frame with one setting of the table angle (per frame). It makes it easy to bevel the inside of the frames with the same bandsaw setting. Its a nice touch in any boat. Good luck with the build; I will keep watching for progress.
Dave

[Bobcat]

How did you all like the leeboards on that design?

[Bob Cleek]

Ditto on the raves about the Marco Polo dinghy! Years ago I had regular access to one. It was plywood planked. She sailed and rowed extremely well for a short wide hull. Definitely go for it!

Caution, however, on using enlarged photocopies as templates. Photocopies rarely, if ever, are dimensionally accurate. While sometimes "close enough," as the image extends out from the center, they will suffer from spherical abberation caused by the curvature of the lens. This is easy to identify if you try to cut and paste a number of smaller copied images of lines together. The lines at the edges won't match up exactly. The larger the copy, the worse it gets. You'd probably be well advised to loft the boat from the table of offsets in Sensible Cruising Designs.

[Geoff C]

This is one boat where a bit of weight won't harm. I'd build ply all over, epoxy glued and CPES'd, and then, expecting some rough landings, I'd put a sacrificial plank bottom over.

If one were to use an outboard, I'd really beef up the transoms, shear strake, gunnels, and hooks so she could work well as a butt boat towing and pushing.

That's a good idea. I've bought some mahogany one by to frame in the transoms, I also have enough plywood to make them double thickness.

I was planning oak rub strips on the bottom.

[Geoff C]

One nice feature of Freeship is that it allows for fast importation of Hulls models, which in turn can be made quickly from the table of offsets. The waterline shown is at 500 lbs.:



It's easier to get the dimensions of bulkheads and building forms from Hulls also. So why use FS? It has the ability to model curved stems, it has more sophisticated hydrostatics, and one can specify the grid dimensions on the panel layout for the plywood. By the way, if anyone would like the FS or Hulls model, send me a PM.

Before marking out the panels, they first must be scarfed. I used a 2" overlap and planed the panels down to the marks. Does anyone recommend one of the scarfing tools made for this operation?





I coated both edges with unthickened epoxy, then used equal parts wood flour and silica to make a glue to bond the two sheets together.



A little plastic under the sheets and a little weight to apply pressure ensures a proper bond. I cover the top of the joint with clear packaging tape over the fresh epoxy to give a smooth surface that won't need a lot of sanding later on.



The weather in New England has been warmer than normal so I'm getting a good jump on this build. The boat has to be done by the end of June.

[David G]

I've always admired this design. Good to see another being built. Looking forward to the fotos.

[johngsandusky]

Sounds like a great idea. I've wanted to build one glued lap ply. But my dinghy dock limit is 10'6".

[BBSebens]

Is a 2" scarf enough? I was under the impression a person should go more than that... Although I doubt the epoxy will ever let go.

[htom]

General rule is eight to twelve times the thickness. Longer scarf bends with less distortion.

[Geoff C]

After bonding two panels together, I marked out lines at one foot intervals, then marked off the position of the bottom and garboard strakes as given by the Freeship panel layout. I drove brads at the marks, then connected the marks by tracing along a batten.



If I were doing it as a stitch and glue boat, I'd cut both sides to the lines, but since I'm going with lapstrake, I'm leaving extra material on the lower edge of each strake.



After these parts were cut out, I bonded the remaining partial sheet of ply to the third sheet. I then marked out and cut out the binder strake and the shear strake.



The two transoms are marked out next.



The two transoms will have ply outer surfaces and will be framed in mahogany. I haven't decided yet if I will use a single or double thickness of ply for the transoms.

Last week-end I bought a 10' mahogany 1 x 6 which will provide the material. I just spent several hours working on the layout in CAD to get the needed cut angles and lengths for the framing, and have it all come from that single 10' board.

A little clean-up with a plane and the strakes are good to go.

[Geoff C]

I had to halt work on the boat temporarily to repair the washing machine for SWMBO. Anyone else have a front loader? Apparently they (mostly) all share a common defect; the mount for the spinning tub is made from a material that dissolves into mush and breaks after 5 to 7 years, causing the washer to sound like it wanted to fly apart. Of course the repair man wanted me to buy a new one for $700 to 1000. but I tore it down and found a replacement tub online for $200. Should be good as new when I get it put in.

Back to the boat. With the ply panels cut out it was time to turn my attention to the transoms. The outer part of the transoms will be Okoume with a frame of solid mahogany. My CAD layout gave me the dimensions for cutting out the parts. These were precoated with epoxy and glued together with thickened epoxy on the assembly table.






When the epoxy had set up, I used the same proceedure to attach the outer transoms to the frames.






It's a little tricky to line up the outer transoms with the frames, clamp them without having them move, flip them over, then clean up the squeeze-out.

Once these were cured, I beveled the faces that would take the planking using a saber saw and sander. The upper edges of the transoms will be given a full (1/2") radius.

The transoms as they stand now:



Now on to the building jig.

[johngsandusky]

Nice.

[Geoff C]

I went to Lowe's and found a couple of straight 2 x 6's and some straight 2 x 4's. The jig is relatively simple, a rectangular box section with the 2 x 4's attached at the station locations. As I am finding out, care taken with assembly here will pay off later. Since I have already cut a "kit" of parts, any misalignment will show up as a poor fit of the planking. A framer's square is very useful for getting things plumb.




Glue and decking screws were used to build the jig. I plan to reuse the basic jig for future projects.




The dimensions of the forms was provided by the Hulls model. I used 1/2" underlayment ply since it is cheap and strong.




The forms were attached to the station locations with sheetrock screws.




I cut angled mounts (30° front and 12° rear) to mount the transoms.



Aligning the two transoms turned out to be a very time consuming task. They need to be located correctly in three dimensional space in addition to being mounted at the correct angle. I temporarily used the sheer strakes as a reference. Needs to go a little to the right, I think...

[P-man]

looking good!

[Thad Van Gilder]

very nice!

[Geoff C]

It's been a busy few weeks. We traveled all the way down the east coast to Cedar Key, FL, to take the sailing canoe to the annual Cedar Key Small Boat Meet. Met a lot of nice people, ate some great food, and had a chance to sail some of the best waters for small boats and sailing canoes. Special note should be made of the terrific Saturday night shrimp boil put on by the West Coast Trailer Sailor Squdron.

When I last gave an update, the bottom panel was attached and I was trying to decide the best way to handle the attachment of the remaining panels. Since I am going to put a layer of glass on the bottom and garboard panels, a lapstrake overlap here doesn't make sense, so I planed a bevel on the respective mating surfaces and stitched them together every 6".





I used the green steel wire sold for use by gardeners to secure plants in place.



Underneath, on the interior of the boat, I lined the seams with clear packaging tape. This will ensure a neat joint without the need for clean-up later on.



I clamped a batten to the outer edge of the garboard plank to ensure it would maintain a fair curve while being glued. This worked great.

[Geoff C]

After the initial glue tabs set up, I removed the stitches and glued along the entire length of the seams. Leaving the final fairing for a moment, I did some trimming of the excess material with a Japanese saw. This saw has been one of the best, most useful additions to my tool kit.



I've debated whether to do the entire hull in stitch and glue instead of the originally planned lapstrake, but doing so will add weight compared to lapstrake, not to mention added time and cost, so I think I'll stay with the original plan.

This hull design really lends itself to a stitched lapstrake approach, so I'm going to give that method a try. The first step is to apply a 1/8" x 45° bevel to the edge being lapped. This is easy to do with a trimming router.



Step two is to use a 5/16" cove cutter to cut a 1/8" x 5/16" channel on the lapping edge. I left 5/16" of extra material beyond the computer generated line that would be used for a stitch and glue type butt join, then routed the 5/16" channel on the lapping edge of the ply.



When I test fit the panel on the boat, voila! A perfect fit. This is going to work out after all.



The other side.

It appears that my experiment of computer generating and cutting a "kit" of parts and assembling them with accurate laps is going to work even better than I thought. This will save a lot of time and improve the accuracy of the assembly.

[dredbob]

Geoff,

How does the stitch & glue add weight over the glued lap? Is it just the weight of the tape along the seams? Or something more?

Beautiful job, by the way.

Thanks,

Bob

[Geoff C]

Geoff,

How does the stitch & glue add weight over the glued lap? Is it just the weight of the tape along the seams? Or something more?

Beautiful job, by the way.

Thanks,

Bob

On the interior I could get away with tape over each seam, but on the outside I would have difficulty fairing/hiding the tape line so I would probably cover the whole exterior with cloth. That would make the boat more ding-resistant but also heavier and more costly due to the additional cloth and resin. Trade-offs...

[Tim Mooney]

There is a Vaitses built Marco Polo Dinghy in the Mystic Seaport Warehouse which has a beautiful bronze double jointed leeboard fitting. The fitting shows in the photo of the boat, Twilight, in the Mystic Seaport Watercraft book (2nd Ed.). The photo in the book shows the leeboards in the outboard position. In the warehouse, the leeboards are inboard and the fitting holds them neatly alongside the topsides. I remember Ben Fuller saying that there would be a tour of the Warehouse during the WoodenBoat Show.

[Geoff C]

Only a month to go before the boat needs to be done, I better get going!

In order to protect the bottom against the inevitable rocky landings, I covered the lower 3 panels with 6 oz. fiberglass cloth. Jamestown Distributors sells it in 50" wide rolls for a little over $6. per linear yard. I applied a coat of thinned epoxy initially, more to come.



Time to install the first set of lapping panels. The fit was perfect. I decided to try West 610 pre-thickened epoxy to glue the seams. I like this stuff; it comes in a handy caulking tube size and has a nozzle that mixes the the resin and hardener as it passes. I found that by putting the nozzle in the freezer after use, I could use it again since the cold temps kept the epoxy from hardening. The color is a match for the West 207 hardener.




I drilled holes and stiched the panels every 6 or 12" as required. This is all it took to secure the panels in place.



The shear strakes went on in the same fashion. It didn't take that long to plank the boat, well worth the effort to get a nice hull shape.



From the rear. The angled pencil line was from the computer generated "lofting" to show where it should align with the transom.



Now comes the time consuming job of filling, fairing and sanding prior to recoating the bottom.

I may install the rub rails prior to turning over the hull.

[johngsandusky]

Cool.

[Geoff C]

Sounds like a great idea. I've wanted to build one glued lap ply. But my dinghy dock limit is 10'6".

This is a big dinghy. Even if you rescale it to 90% of its size it would be 10 1/2' x 4' x 16" high amidships, enough to hold 500 lb.

[johngsandusky]

An interesting idea, thanks. I cut down my current dinghy to fit. But like many of us, I'm always thinking ahead to the next boat. Of course 500lbs is me and one brother, but that applies to any modest dinghy.

[Geoff C]

Pardon the slight thread drift. I wasn't able to work on the tender last week-end because we were up in Maine doing a "blitz" bottom redo on Blitzen.

Before:



And after:



This year I'm giving VC Offshore a try. We race every Saturday at the mouth of the Damariscotta River, in case you are in the area.

While we were working on Blitzen, Walter Wales and his wife, Woodenboat Associate Editor Karen, dropped by to admire our work (not really). Actually, they were there to launch their recently acquired 26' double-ender, Lucy, built in Denmark some 45 years ago. It's a real stunner.




A Bristol boat in bristol condition.



They were kind enough to let me check it out. It sleeps three and has a teak lined cockpit.

[Geoff C]

Back to the subject at hand.

Being impatient I thought it a good time to roll the boat over and work on the inside for a while.



It appeared that only minor clean-up would be needed.

Looking toward the bow:



After sanding, seam filling, and epoxy coating:



Still more sanding:



Since I will be using removable floorboards, I won't put down a layer of glass cloth inside. Okoume ply doesn't need glass cloth to keep from checking, just a coat or two of thinned epoxy. I did cover the first joint with glass tape, however.




The frames are next.

[johngsandusky]

Loved the Maine pics and the update.

[Geoff C]

The original plan calls for dory-style frames set every foot along the length. I'm keeping the dory frame construction but doing away with all but three of them in keeping with the anticipated use of the boat.

The frame construction is pretty straight forward. The front and rear frames required sanding at a bevel angle to lie correctly on the bottom. I glued up the lower three pieces of each frame first.



Detail of the frames. These will be under the seats so most of the frames will be out of sight.



Before installing the upper part of the frames, I wanted to clamp the rub rails in place to ensure a fair curve on the shear strakes. Since these are vertical, and there is a pronounced curve to the shear line, the rub rails must bend in two directions to fit. The original plan called for 1 3/4" x 3/4" rails, I'm going to use 1 1/2" x 3/4". There is no hope of using oak or ash without steam bending, but I can get Douglas fir to take the curve. Yes, I know it is soft. Yes, I know it is prone to splintering. I am going to use a dinghy bumper over it so it should be just fine, and I rather save the weight.

I pre-radiused the outside edges of the rub rails. Hey, every little bit helps when you are trying to bend this stuff.



With the rub rails clamped on temporarily, I glued the upper sections of the frames in place.



Final gluing of the rub rails took a jillion clamps, but I got it to work.



Next: Seat risers and knees.

[johngsandusky]

I used solid fir as new sheer planks on my ply dinghy. No rubrails, no inwales, just rubber on the outside. Plenty stiff, no damage to dink or mothership.

[Geoff C]

I decided to notch the frames for the seat risers rather than cut the upper edge of the risers at an angle. Seemed to look better. I used the Japanese saw to cut out the notches.




I epoxy coated the risers and glued them in place. Since I lacked a clamp ruitable to hold them in place, I used a screw at each of the center frames. The "spring" of the wood held the risers to the front and rear frames. In case you are counting, these are the first two screws used in the construction.







My wife drove in to Cambridge to get a 12 ft. mahogany 1 x 12 board for the seats. Beautiful stuff. With the excess material I cut the four knees that would be needed.



They are fairly easy to make since one edge is vertical and the angle for the other edge is taken from the transoms.

[Geoff C]

Here are the bow knees being glued in:




And here are the stern knees:



The inwales are clamped in place temporarily.



If the inside of the boat looks a little shinier, it is because it now has a coat of varnish.

To get the length of the inwale exactly right, I cut the end off the inwale and kept cutting right through the knee, so a line-to-line fit could be achieved.



Now the inwales can be glued.



Time to turn it over and give the bottom a coat of one-part polyurethane.

[Geoff C]

Next up is the installation of the skeg. The size was taken more or less from the plan and cut from a piece of white oak. A pencil on a spacer block was used to trace the correct curvature.



After tracing the curve, I cut to the line on the bandsaw.



Gluing it on required the assistance of some idle bricks and a worn out battery. You never know when you might need stuff like this.



When the skeg set up, I gave it another coat of paint. I'm rolling it on with a mini foam roller.



It's starting to look like a boat!



In order to set the waterline correctly, I borrowed a laser level from a friend. Isn't technology wonderful?



That's about where I am tonight.

Next; seats, anti-fouling, oarlocks, done!

[johngsandusky]

Still looks great. It's already a boat.

[Geoff C]

Thanks for the support, John. You've made the last 5 comments on this thread, where did everyone else go?

Using the laser level it was a simple job to mark the waterline, after the boat and the tripod for the laser were moved around a few times, of course.



A couple of coats were all it took to give good coverage with the Racing Bronze. Those inflatables at the dinghy dock won't be able to keep up now.



Using some scap mahogany from an earlier project, I cut out some mounts for the oar locks. My wife said to make them beefy, our oldest son can really muscle those oars.



Just making it up as I go along, here:



The finished product in place. Quite a contrast in the wood colors.



Bailey from the back:



I'm going to make some floorboards tomorrow.

[JimConlin]

A very nice boat and a good job.
That design has been on my 'top ten' list for years. You've bumped it up a few notches.

[johngsandusky]

Thanks for sharing your build. Others are watching in silence.

[htom]

And admiring. One of my very favorite designs.

[Geoff C]

Now that I've had a chance to use it in action, I thought I'd give an update.

The boat is very stable under foot when climbing in from the dock or down from a larger boat, surprising for such a light boat. I'm very pleased about the stability. It's also more stable than the previous flat bottom rowboat.

Rowing is very easy due to the high rowing position and the low wetted surface. When going full speed you can raise a pronounce wake astern. Very manouverable, of course. Strong winds will try to blow it around but it is easy to hold course because of the responsiveness to the oars.

Without the seats installed, it was very easy for two people to pick up and put on the roof of our van, so that target was met.

What worked well:

* The precutting of the parts from the computer model worked well, I would do this again.

* Machining the laps with a router rather than planing them worked well also, the fit was perfect.

* Using the West Six10 epoxy-in-a-caulking-tube to glue the laps worked as expected, there were no runs or drips to deal with on the inside of the hull, all the glue stayed in the joint. Well worth it for the time savings alone.

* Not having a chine to bevel or fillets of epoxy to sand and tape was nice also, and saved a lot of time. I did put tape on the first chine joint, but that was more to keep water out of the joint since it didn't need the added strength. May not have been necessary. I like the stitched lapstrake method a lot.

* The laser generated waterline was spot-on, nothing to change there.

* The frame spacing of 36" works well, it allows you to place your feet on a cross piece while rowing.

[Sailor]

How about what didn't work or what you didn't like? That way we can take your lessons learned away from the project too.

[htom]

:big smile: The best of "form follows from function". She's beautiful.

[skaraborgcraft]

Thats a fine dinghy and a great job.Thanks for sharing.

[Ian McColgin]

Finastkind.

I've rowed one in a goodly wind and it's surprisingly weatherly. Nonetheless, had I one I'd want to make a "sideboard" or a pair of leeboards with different attachment than LFH shows to allow for rowing across a high wind.

I've not rowed another boat that handles so well whether laden or light.

[CundysHarbor]

Nice job of updating a classic LFH design.
Dave

[Geoff C]

How about what didn't work or what you didn't like? That way we can take your lessons learned away from the project too.

Fair enough. The one lesson I learned was to make sure, when stitching the laps, to check inside the hull to see if the gap in the planks has closed up completely when the stitch wires are tightened.

Here's what I would do differently next time:

* Get a scarfing jig. My scarfs were not very accurate and needed filling. A waste of time, money and added weight.

* Put limber holes in the front and rear frames. I thought the water would find its way under the frames but I guess I sealed them too well.

* Make more accurate cuts on the transom frames (see scarfing comment above). Now that I have built it once, I know exactly what the angles need to be. It might also be possible to fit the transom frames after the basic shell is glued up, at the same time the frames are fitted.

* Make the frames more like the originals, with some curvature to the upper part of the frame where it is seen above the seats.

* Make the rub rails tapered toward the ends as called-for on the plans.

These five comments are in-part due to rushing things a bit due to time constraints. Of course, no one looking at the boat notices these things.

There are several things I changed about the design to adapt it to my anticipated usage:

* The original design called for 10 frames. I cut this down to 3, and the boat is plenty strong as-built. The frames I used were the third, sixth, and ninth ones on the plans. I'm not wishing I had added the other seven.

* The rear seat was originally on the tenth frame, so it is now on the ninth frame, a foot further away from the transom, which helps center the load.

* The original was designed for (12" wide) solid planking, so the bow comes out a little high. Since I did not have this constraint, I extended the bow transom downward a few inches which adds buoyancy forward and increases hull speed half a knot due to the added LWL.

* I did not use the original movable center seat. With three seats and two rowing positions it is not difficult to balance the load. All these changes have worked out well.

The sail rig:

I am going to give the leeboards a shot. I may use a bolt and elastic stopnut to secure them, since this has worked well on my sailing canoe. I am also going to add floatation foam to the underside of the seats and secure airbags to the seat risers. The eight bumpers are also part of the floatation plan. I have not made floorboards yet. I will probably do so when I get the sail rig finished so as not to have to sit in any water that might find its way aboard.

[johngsandusky]

Sounds and looks great.
Floorboards are a good idea, but I don't like sitting on the floor of my dinghy. When sailing I have used a board between the aft and middle thwarts to keep my butt off the bottom.

[Ian McColgin]

Nice adaptations. I think the thwarts and seat riser make a fine substitute for frames but I also think that epoxied seams with plywood planks does the job. One would surely need the frames as designed if the boat were dimensional wood and no center thwarts.

LFH did away with the two center (rowing) thwarts because the original went over a skylight. Inspired by that, I took out the thwarts in my dink and really like the uncluttered arrangement. Instead of a purpose made little stool like LFH drew, I sit on an waterproof Pelican case that I use to protect my kit anyway.

I always thought this boat would go well in considerably lighter plywood. Nice to see she turned out so very well.