designing a fast rowboat

Funnily enough, I got a tin of dark bottle green International given me with a boat I bought and happened to have a tin of white too. I thought the green was too dark so mixed the two and came up with a turquoise. I now use a BS 4800 turquoise which you can get mixed in auto or Dulux....

Don't worry about leaving 'rusty bits' - it won't, unless on bare wood. I used to finish racing shells in clear varnish with this technique and it was spot on. Never ever had a problem. It is also a good way of getting to abrade the small low spots when you really don't want to cut further with wet and dry, ie the next coat will fill it in anyway. That is why it is important to degrease with thinners or acetone. The grey 3M scourer type pads are not bad either and non metallic but not quite as fine as the 0000 for ultimate finishing.

After all you will be degreasing or at least wiping with a tack rag prior to application. It does not take much to get any stuff off, in actual fact the wool tends to ball up on itself and not fracture too much anyway. A quick vacuum or blast with compressed air even a good brush will get rid of the main dust and grit.

Good luck with finishing, glad your keeping to that colour.

 

Ok, cool. Thanks for the tips.

 

Dialing in the #'s

After a few iterations, here are my numbers:

Cp = 0.58
Volume Displacement = 306 lbs
Center of Buoyancy = 53.9% aft
Wetted Surface Area = 27.74 sf
Waterline Length = 16' 11 1/2"
Maximum Waterline Beam = 27.7"
Water Plane Area = 24.5 sf
Center of Flotation = 53% aft

I'm happy with everything but I wonder if the displacement is still a touch high. I figure:
boat 75 lbs. I'd like someone to build in 6mm if they want, should be less at 4mm plank which will be my boat; rower 200 (me) to 225lbs max...I want a big guy to be able to row. I'd like to be able to take a few pounds of gear. Oars 5 lbs.

So, I figure I need volume for 275lbs up to 310 #. But should I optimize more? I could take more out of the draft and get 300#. Or maybe leave this extra as a safety factor?

 

Your call, but in the interest of saving work how's this for reasoning?

If you have enough volume for 310 and you only load it to 275, it will float a bit higher in the water, which will reduce wetted surface, which will make you go faster anyway.

The difference in draught between the two figures (275 vs 310) is only going to be around 1/4" anyway.

 

I forgot to add that if you finish with the very fine wire wool method, you should put a couple of coats of satin polish on top. This is important to seal the surface from picking up 'scum' off the water surface, and it helps improve the frictional resistance. It never seemed to slow those sculls from the results obtained, even in World Championships!.

Best wishes for your new boat.

 

Ok. Any particular type? I assume you'd want something that did not contain silicone.

 

I'd definitely go silicone free. I can't remember the exact brand, but would go with a satin carnauba based wax. If you need to touch up (paint wise), a quick wipe with acetone will remove it. I do know that trying to get a grip on a carnauba waxed foil after a capsize is .... interesting...

There are some automotive satin carnauba waxes for satin paintwork.

 

Looked up some of the automotive satin waxes available locally. Damn those things are expensive. I'll probably just rub the boat with the arse end of a candle and call it shiny.

 

I've sorted out a local product I think will do the trick. It's actually made as a gun stock polish, and is based on carnauba, beeswax and gum turpentine. No silicone. I did a quick test by steel woolling, then polishing, a paint stirring stick (had undercoat all over it) and leaving it in water overnight. Seems to be fine. Still had a satin finish when it came out of the water.

One question: how fine did you go with the wet and dry before the steel wool? I'm thinking, based on tests, that there wouldn't be any advantage going much finer than 400, since the wool seems to sort out anything that rough anyway.

 

Hey, phase 1 is done for the Drake Race. I need to get to work on converting the SLRS Annie model to lapstrake. Then I'll cut both boats quarter-scale and build models. I'm GOING to build some rowboats in 2015!

More pics on my FB page, too.

 

NoEyeDeer, What do the sliding seat olympic type guys use. if anything,. They race over 2000 m and its all about name for the boat builders. So anything legal is OK. and .01 % is still quite a bit. The british 4s in Greece won the final by 150 mm. after 2000 m.

 

I like it. Nice job.

 

I have been designing a row boat for rowing on estuary waters, or possibly the open sea in calm weather. (Yes - another one - there are plenty already described here) Mine is to be 4.5m long and will have a sliding seat (although this can easily be locked in one position for fixed seat rowing if preferred). I realise that 4.5m length is rather short for a sliding seat rowing boat, but I wish to restrict length for transport and storage. I am hoping that it will be a reasonably nice boat to row, but it is not intended for any kind of competitive rowing. It is to be suitable for one person rowing on their own or one person rowing with a second person as a passenger. I soon found that two oarlock positions are necessary to get anything like reasonable trim both with and without a passenger. The waterline beam with one person is 645mm, this increases to 735mm with two on board. There will be folding outriggers to support the oarlocks at a suitable spread, which most people suggest is about 1600mm. My software tells me that the weight of the boat with all equipment but no persons on board will be about 38kg (84lbs).

Although I have often rowed to provide auxiliary propulsion for small sailing boats, I have no experience of rowing a purpose made rowing boat so I am a bit unsure about suitable rowing geometry. There does not seem much point in my making this an experimental research project since rowing geometry must by now be well understood, at least by the experts.

I have looked at a few websites and I note there are some slight inconsistencies - I summarise as follows:

John Welsford says:
Seat at least 200mm above heels (others say less than this, but John is thinking of a less agile rower, which I probably am)
Oarlock 220mm above seat

Angus Rowboats says:
Seat 150 to 200mm above heels
Oarlock 140mm to 180mm above seat

Durham boat company says:
Oarlock 220 to 240 mm above waterline
Oarlock 160mm +/- 15mm above seat

There is general agreement that spread (distance between oarlock pins) should be about 1600mm, foot plate angle should be about 40 degrees and oars should be about 2895mm long (9 foot 6 inches).

The three websites above vary a bit with regard to the oarlock to seat dimension. My present drawing shows the oarlock 174mm above the seat which fits in with the recommendation of Angus Rowboats and the Durham boat company, but it is a bit less than John Welsford recommends. If necessary I could easily change this dimension by altering the design of the folding outrigger, but do I need to? For my current drawing the vertical distance from the water to the oarlock is 358mm with one person on board, quite a lot more than the figure from the Durham boat company, but they may be thinking only of racing boats for flat water rowing, I can imagine that one might need the oarlocks higher off the water for estuary/sea rowing.

Has anyone any thoughts on the above, or is it already covered somewhere in this long thread?

 

Durham is talking about racing sculls and sweeps, so their figures reflect that. Welsford is talking about high-sided fixed seat boats for open water, so his figures are considerably different.

Angus boats are sliding seat, but meant for open water, so would probably be the best guide for you. My 2c.

With your narrow waterline beam you'll preferably keep the CG low for stability. Personally I'm fine with a seat 150 mm above my heels, and I'm in my fifties. Just mock it up and see what seems comfortable.

 

There are a lot of interesting papers at biorow. You have to hunt around but this one may help:

http://www.biorow.com/RBN_en_2014_files/2014RowBiomNews09.pdf

Also, assuming you are using the Concept 2 oarlocks and pins, you have maybe an inch of leeway to raise or lower the oarlock with removable plastic washers so you can play around with heights once on the water.