designing a fast rowboat

It's a variation on the wineglass transom . . . I don't think it's particularly attractive.

 

Yes, that's what I mean -- isn't there less drag in a tapered vertical stern like that than in a flatter cut-off one like the Firefly has?
To give examples at each end of the spectrum: The upside down hull here has a flat (planing?) stern http://www.metalboatkits.com/16_foot_skiff/16footskiff.htm
versus say the tapered-to-vertical stern of this:
http://www.nauticexpo.com/prod/wint...creational-quadruple-sculls-22349-130933.html (minus the big rudder).

 

If using plywood planking on any 'chine-built' vessel these days, S&G really makes more sense than an internal chine log in a large proportion of boats.
1. No fitting, twisting, planing.
2. S&G drains perfectly when done well.
3. Better 'fastening' than a mechanically fastened chine.
4. Chine logs are famous for rotting in the ends, are heavier to start with and more so when they get wet.
5. Easier to clean out the boat, fewer cracks and crevices.
6. If design requires additional strength at chine, add an outer chine that will protect from chafe as well.
7. Good to use 2 layers of very light cloth on inside and 3 on outside.
I cut these diagonally on the bias so all fibers cross the joint, and at 2" wide, 3" wide and 4" wide, and just put them all on pretty much at once, after the filleting is done.
Pre-cutting the pieces and rolling them on individual cardboard tubes, application is not too hard.
Various widths makes it easy to finish up with a tapered edge of the cloths.
Again, scrape (very sharp scraper custom made to fit the job, sharpen every 2-3 minutes), don't sand, and don't let it set too long before you do, and all will be easy and need much less sanding, almost none if you do it right.
The real secret is to thoroughly mask off the areas alongside when you are doing the filleting, use a radiused squeegee, and I personally find that WEST with 'Filletting' additive (the brown stuff), over resin-primed ply, goes quickly with little fairing needed.
Instead of sanding, make a steel radiused scraper from a piece of saw blade and scrape the epoxy before it gets real hard.
I hate sanding.

 

At slower speeds an immersed transom will usually have higher drag than a "similar" boat without an immersed transom. Key is immersed. If the transom is above the water than it doesn't affect trag. Based on the photos I've seen of the Ken Bassett Firefly its transom would normally be above the water.

 

Tallman: the transom of the Firefly is above water as David notes so it wouldn't drag. I'm not familiar with it but the boat looks to be designed for planing, which would be appropriate for a class sailing dinghy; the flat bottom and transom would aid that. The rowboat with the wineglass transom linked in your earlier post would obviously not be intended to plane; FWIW sailboats with wineglass transoms - typically with deep keels with ballast - also don't plane (except on a tsunami)

I have a small row/sailboat with a flat bottom and transom; it rows very easily solo when the transom is above water. It starts to drag when 2 up but no doubt would still plane.

No matter what a transom looks like, for rowing where there is not enough power for planing the flat part must be above water level; what it looks like from there on up is not all that important except in heavy weather or surf AFAIK.

 

Which Firefly?

- the row boat designed by Ken Basset / Onion River Boatworks, plans sold by WoodenBoat
http://www.woodenboatstore.com/18-Pulling-Boat-Firefly/productinfo/400-121/
http://vimeo.com/36628530

- the sailing dinghy, popular in Britain, designed by Uffa Fox
http://www.fireflysailing.org.uk/

- 10 foot dinghy
http://www.nauticexpo.com/prod/shea...ats-wooden-construction-kit-20959-250149.html

 

The "class sailing dinghy" I referred to was the UK one design class boat, I got it mixed up with the Ken Bassett design, but I think my post was generic enough to apply across the board.

 

progress

We are back to regular rowing every Sunday. Slowly sorting out the boat and making minor changes. It is getting better and easier to row. Our conclusion is that the boat needs a long keel similar to what you would see on a canoe. A little change on the aft rowing station will help there. The stern forefoot (?) needs to be cut away a bit to reduce the steering effect when the boat lists one way or the other. Last Sunday we rowed about 41/2 miles and for over 1 mile we held between 5.8 knots and 6.3 knots. very encouraging! I'll row the Essex River race this Saturday solo, and on June 2nd we'll row in New Bedford double in the Whaling city rowing clubs row for the bay. It's a short race: 3.75 miles on a triangular course. The third leg puts you in the edge of the shipping lane and you need to keep your eyes open so as not to get in the way of an inbound fishing trawler. They keep their eyes open, the dangerous boats are the pleasure boaters who seem to be totally unaware of their surroundings. A good race with a nice barbecue afterwards.

 

race

Essex River race was great! Clear and sunny with temperatures of 70 degrees and very light winds. 135 boats, mostly sliders, kayaks and sea skis. A fair number of traditional boats, maybe 40. Fixed seat singles, my class, had about 16 boats. I managed 4th place with a time for 6 miles of 1hour and17 minutes and a few seconds. Knocked 3 minutes off my best time. There are things to be done yet: slightly longer oars with long straight blades will allow me to use the dory stroke and gain some speed. I've borrowed a pair of straight blade oars and got about 1/10th knot better speed with them. finishing off a pair of the oars i've started is now a must. Also, a seat pad with cut outs to mimic the seats that the sliders have will help fight fatigue and discomfort.

 

Glad to hear it went well. Your tailbone will appreciate that cutout in the seat. I got a seat from concept 2 and spaced it up from the bottom board.
What are the dimensions of the oars you're working on? I think in a race you're using the dory stroke whether you mean to or not.
I picked up an old Easy Rider Cormorant with oarmaster rig off craigslist last Saturday. It will cartop easily, and can be paddled, but I still prefer my wood fixed seat boat.

 

what

An easy rider cormorant? What the heck is that? i've never heards of it. Right now, I'm rowing with 8' oars that have quite a pronounced spoon in the blade. They tend to catch as I try to feather them up out of the water. With the geometry in my boat,, My hands are about 4" apart at the high point in my pull and seperate way too far at the finish of the pull. The new oars are over long right now but I want 2" more inboard and enough outboard to maintain the same ratio that I have now. I haven't done the measurements yet but think the length will come out around 8' - 6"to 8". the oars are made out of white cedar and are very flexible. I'm going to put a layer of glass cloth on the whole oar to stiffen and strengthen it. Just need to find the time to do it. I borrowed a pair of straight blade oars and practiced the dory stroke a bit and the GPS showed a .2 knot speed increase. If I can do that for an entire race, It will get me up nearer to the leaders.

 

Cormorant

Not my favorite fowl, but here's the rig including an outrigger to calm my nerves when an oar dives in the boat wakes. Will try it out in the next few days. Sorry about the pic. I shot it at 8:45.

 

Oarmaster Sliding Seat

I didn't like the way the oarmaster unit felt in the cormorant so I put it in my old boat. It dropped right in nicely but the feathering oars and 64" spread still felt awkward. I took off the riggers and tried my old fixed oars with 45" spread with the sliding seat and it felt great. First time out with this setup I did 3 miles in 33 44 by my gps without working too hard. I didn't use to feel I wanted a sliding seat, but now I'm a convert.

 

Yesterday was the second Round Canvey island race organised by Benfleet yacht club, i launched my new 18ft Skiff for the first time on the day. In fact i screwed the last fitting on 5 minutes before the start, need to stop doing that!
She is an updated Sail & Oar version of my old boat but with a buoyancy tanks moulding, Despite making a real effort to keep her light there is a weight penalty as i reckon she has got to be over 350 lds.
Plenty of competition from sliding seat coastal four, Fisa coastal pair, three different 4 oared gigs, kayaks & some sailing boats, its a race that allows sailing as well.
Not enough wind for us to sail for most of it so it was out with the oars. First time in a fixed seat Skiff for 9 months & it was bloody hard, My boy has bust his ankle so two of his mates stepped in, they got to swop over, the old geezer had to row. The after race beer was pure nectar!
Fastest boat round the 14 mile course was the Coastal four from Gravesend RC in 2hrs 2mins, the Fisa pair took 2hrs 8mins, followed closely by the Gigs.
A strong lad borrowed a Mondego single & did it in 2hrs 18mins, boy did he have some impressive blisters!
Will post a link when the photos are up.

 

good news

Keith, congrats on your new boat. Post pictures when you can. Also, how many miles was that race, give us details on the course. I am kind of amazed by your estimate of the weight of your boat. 350 lbs sounds crazy heavy for an 18 foot boat. Our 19' boat weighed about 250 by our best estimates and no effort was made to keep her light. it has a plank bottom with heavy sawn frames and plywood planks. I did the annual great river race here in Marshfield on August 18th. Small field of boats with only a few fixed seat traditional boats. THewinner was a Herreshoff "Althea" design. It is a professionally built boat and is a thing of real beauty. the crew that rowed it has been beaten by me and my brother for 10 years straight. They did the 7 miles in 1 hr 2 min and change. we were in at 1hr and 6 min and change for almost 5 minutes behind them. We were pretty happy. Knocked 3 min. off lasr years time and on the way back ot being competitive. My brother has almost come back from the saw injury to his hand and is rowing stronger each week. Sept. 16th is a new race: the Minot's Lighthouse Roundabout. I don't know if we will do it. The course is very difficult with out going an in coming lanes almost overlapping. The chance for collisions doesn't make for good racing. The race is all in the open ocean and the part around the lighthouse is famous for bad conditions. There are ledges every where and good navigation as a must. No decision yet maybe next week.