designing a fast rowboat

This may be the perfect place to post my question with all the talk about length, beam and chines. If I found a nice design, but want the same boat longer, can I just space the stations a couple inches further apart. For example, the Whitehall "Liz", has a nice looking hull. I'd like to stretch the designed 18 foot length to twenty feet, and leave the sections the same. Is that going to require some lofting to get the lines fair again, or will it stretch OK.

 

Merry Christmas from the Hawaiian Islands

 

This may be the perfect place to post my question. If I found a nice design, but want the same boat longer, can I just space the stations on the building jig a couple inches further apart. For example, the Whitehall "Liz", has a nice looking hull. I'd like to stretch the designed 18 foot length to twenty feet, and leave everything else the same. Is that going to require some lofting to get the lines fair again, or will it stretch OK. Do you think there might be a limit as to how far a design can be stretched? I'm curious what opinions are out there. Merry Christmas everyone.

 

Yes, re-spacing the stations works well. At Swiftships in Morgan City, Louisiana, that's how the 85-foot aluminum crewboat became the 100-foot aluminum crewboat, an 18% stretch.

 

spacing stations

Rowboat 70, Thanks for the reply regarding station spacing. This possibility opens up a whole bunch of possibilities.

 

Jon thanks for the update. I have heard a lot about you so hope to meet in person someday. Would be fun to kit out your boats in the computer sometime but I got a few personal projects to get off the table first.

Cheers

 

A good rule of thumb is a 10% stretch is OK without relofting, just space out the stations. With a rowboat I think 10% is comfortable and you should have no problem at 20'.

You'll pick up some wetted surface area...is still a solo boat? You'll be a little heavier too but resistance should be lower with the longer waterline length.

 

old engines

Jon states that the engine is getting old. Just for the record, he is still the guy to try to beat around here. The stability issue is very real. Our 20' boat is very tender and requires a lot of energy to keep her on an even keel; energy that would be better put into forward motion. Getting set up to bead and cove about 3000' of 1" X 5/16" western red cedar. Got the router and bits, now must make a table, fence and hold-down fixtures. the goal is a bit larger version of a Peregrine Rowing boat for two rowers and seaworthy enough for our races. My old engine is slowly recovering from prostrate cancer surgery. We did the November race and had a time in the middle of the pack that would have been a winner not too many years ago. the competition is getting better and has invested in some big-name designers and builders to get faster boats. Kind of a disappointment today: no New Years Day row for the first time in almost 20 years. Really missed it. A happy New Year to all and good rowing!

 

This has been a very informative thread. There are some very knowledgable people posting here, so this might be a good place to ask some opinions.

I'm planning on building another rowboat for use on the Great Lakes. I'm a very large and tall person who used to be strong. I have built and rowed a Bolger's dory (GLD) and a Welford Molleyhawk and too many Kayaks and Canoes. I would like to have something that is a fairly fast rower (an improvement on my other two efforts) but at my age I'm not going win any races. I would like perhaps to at least enter a race at some point and finish.

After a lot of "looking around" I have ordered the plans for the Westlake Handliner "Brightsides" http://www.westlakeboats.ca/. I really like the looks of this boat and think it could handle Lake Huron (on calm days!). I plan on lengthening her out a couple of feet to around 17 feet, for my size and to give her a little more top end speed. I also plan on trying to keep the weight down on the build.

Any thoughts on the choice of boat and the modifications.

Thanks Ted

 

Nice looking boat. Should be a real nice rowing boat. Definitely needs to be lengthened and built as lightly as possible. What are the recommended scantlings? My 17' wherry has 4 mm ocumme side planks and a 6mm bottom plank.

Jon

 

Longer is Better

This is the era of the personal watercraft (PWC), which, according to the U.S. Coast Guard, is "not a boat", and is therefore exempt from the Coast Guard regulations limiting the amount of horsepower that may be installed, based on the size and weight of the boat. Due to PWCs, there is no more smooth water. Wakes converging from different directions create a mix-master of square waves. Seakeeping is a function of length/displacement. My rowboat is a Minnesota IV canoe that is 23 feet long and weighs 65 Lbs. The drop-in rowing rig weighs 55 Lbs. I weigh 200(+). The oars, emergency paddle, life jackets and the cooler bring the all-up rowing displacement to about 330 Lbs., which is featherweight for a 23-foot boat. I need to use my boat to keep rigor mortis away, and to keep the cob webs out. A long, lightweight boat can cope with today's unfortunate circumstances.

 

Jon, the designer has her 6M all around with a lot of glass. I don't know the exact amount as I have not got the plans yet.

I do think that an extra couple of feet will improve the appearence as well, as performance.

 

After more than a decade of use, lots of rowing and bouncing around on a very stiff trailer my wherry has had no structural problems. We could also talk about the embarassing list of very hard things that I have rowed into without damage but that's a story for another time. The exterior has 6 oz cloth (the new boat will have 4 oz.) and the interior seams are taped and framing is minimal. This is a very strong method of construction. I would talk to the designer about using 4 mm for the side planks.
My opinion has formed that to be fast, boats should be as light as possible. It also has the advantage of making the boat easier to move around in the back yard when there never seems to be anyone around to help.
The boats that win in our class in the Blackburn Challenge are always quite light, usually around 60lbs.

Jon

 

Hoss10 be sure to check out my Drake rowboat. Sorry, self promo over.

You can also build very light without fiberglass. I think it takes a lot of experience to build a boat with fiberglass that is as light as a glued lapstrake boat. This is because most home-builders typically over saturate the glass, adding weight to the boat.

I think glued lapstrake in 4mm ply makes a better and prettier boat than stitch and glue with 4mm and glass.

Light is definitely key. Building light is an art form. Every decision effects the eventual weight of the boat: screws or no screws? What kind of paint? How much epoxy is going on? What timbers are you using and where? How about the hardware?

 

I have looked at your Drake, Clint and I really like the looks but I was concerned about it's capacity. At it's DWL it's capacity I think is 350 pounds. I'm a big guy 6'5" and... well my dog and I would put it at capacity. Would it be up to additional weight?