Welcome! Log In Create A New Profile


Two passengers or four?

Posted by Sandy 
Two passengers or four?
March 25, 2021 05:40PM
I'm trying to get back in the shop again, after six weeks off with some Covid-related health problems. Things are looking up. I've had both vaccinations and for totally unexplained reasons my energy is flooding back. This is common among Covid long haulers. Even though nobody knows why.

I'm working on a big white water boat. Mine has has gunwales about 18' feet 9" long. Something like that. If it rows well I'll measure everything up, mock it up a second time and make plans. It's wide too. Almost 8' feet across the oarlocks. It will need a rower's seat a few inches higher than normal plus ten or eleven foot oars. I have a pair of ten footers. I have a hunch they will work just fine.

I will never row this boat with more than two passengers but I want it to be able to take four so it can compete with the Briggs. The Briggs is maybe four or five inches longer and it typically puts two passengers way up front, a rower in the middle and two more passengers way in the back. Briggs boats are built for Grand Canyon runs with four passengers and no camping gear. Tents cots food and cooking gear typically come along behind in a support raft.

I think all dories row better when the payload is concentrated closer to the middle of the boat, rather than out at the ends. I also like wider boats.

The first photo here is a huge boat belonging to AJ DeRosa and his partner Dutch (the boat was designed by Cyrus Happy) that has 20' foot gunwales and a 69" inch bottom. It has two rows of three seats in the middle, with the rower behind all of that. I've rowed this boat, albeit without passengers. It is surprisingly easy to row. I'm taking my inspiration from this Cyrus Happy boat.

This is this morning's mockup for four passengers. The actual seats will be close to two feet higher up, on top of a deck. This does provide a preliminary look at the layout.

...and here is this morning's mockup for two passengers, with the rower a few feet closer further forward. Hence the need for a sliding passenger assembly.

To make all of this work I think I'll build a depression in the deck X" inches wide and Y" inches deep to make a place where two passenger seat benches and one rower's seat can be positioned, in a manner that allows the whole thing to slide forward and back as a unit. For those like me who will never row with four passengers the front passenger seat area could become a place for a big expedition cooler and water cans instead of passengers. I'll also, alas, for the groover, probably behind the rower.

Most white water boats build a passenger seat station that assumes the passengers will be sitting with legs straight down, as if they were sitting at a dining room table. I'll build the floor of the sitting areas so the passenger's legs are positioned more like they would be in a car. Or perhaps even in a sports car.

All seats will move forward and back as a unit, to some degree anyway, so the boat can be trimmed and re-trimmed for any load The oar lock pins will be fixed on that movable frame--but where the rower's foot braces and rower's seat are will adjustable with respect to the frame as a whole. Now I can accommodate two passengers or four, or a short legged rower or a long legged rower.

I think I'll do all of that by welding up an aluminum frame somewhat like a raft frame. Under the deck a white water boat needs bulkheads so a puncture to one spot in the hull doesn't sink the boat. I want to limit the number of bulkhead compartments to a small number of relatively large compartments. Perhaps three bulkheads and thus four chambers.

How access to those bulkhead spaces below the deck works--with a rowing/sitting frame on top--is yet to be determined. I'm working on it.
Re: Two passengers or four?
March 31, 2021 03:18PM
If you 2 passengers, why not just put one in each bench each seat, fore and aft tandem style? If you have 4, put two in each bench. Then you don't need the sliding passenger seat assembly for trim.
Re: Two passengers or four?
April 01, 2021 12:03AM
:=)) Because I want the weight in the middle of the boat rather than out at the ends. For a lot of reasons.

In a high rocker boat passengers out at the ends are high up rather than low down. That makes the boat unnecessarily tippy.
Weight in the middle is more side to side stable and easier and quicker to turn.

Traditional Oregon dory builders know this. They have always put the payload as two or even three passengers across on a front seat relatively far back from the downstream end of the boat. That's how they perform best.

Two rogue traditions changed that: fly fishing and the Grand Canyon. For fly fishing you have to separate the two passengers. The boats become less maneuverable but that's the price you have to pay. The Grand Canyon is an odd story. Martin Litton paid Keith Steele to make a decked boat big enough to take four passengers. The Susy Two. Keith wasn't into it. He chopped in 15x48 boat in half and stretched it out to 19 feet long instead of scaling it up proportionately, so it was a long skinny boat with passengers at both ends.

He didn't want to build any more so Martin Litton got Jerry Briggs to do much the same. Not many Grand Canyon runners have ever tried to change anyhing. They build long skinny boats that are annoyingly side to side tippy. If a 19' foot boat had been scaled up proportionately, from the original Keith Steele boat, it would have been 57" inches wide not 48.

If it had been scaled up proportionately it could have carried all four passengers in the middle instead of the the ends. Which is how Oregon dories are supposed to work.
Re: Two passengers or four?
April 01, 2021 04:30PM

I was thinking with 2 or 4 passengers, the center of gravity of the load is roughly the same (black X). The magnitude of the load of course doubles with 4. However, the beauty of your idea of putting the load in the middle of the boat is it should be near what we can call the center of buoyancy. I'm thinking the trim might not change much.

Say you are rowing the boat empty and have it trimmed for only a rower. There is some natural point in the middle of the boat that you can center cargo weight and increase draft but maintain trim regardless of the magnitude of the load. If you can center the passengers around that spot you're good. Unless 3 passengers...
Re: Two passengers or four?
April 01, 2021 08:06PM
Gotcha. Cool.

I'm working with OSB today. I can afford to make mistakes with wafer board. I'm going to have to take that empty boat hull to a local lake next few days so I can put a 4' foot level in it, while it's afloat, and find the precise center of the boat. I do that on all new hulls. It gives me more confidence about where to put the seats. Even then I'm a still a bit chicken feces, and *still* make everything adjust a little, forward and back.
Sorry, only registered users may post in this forum.

Click here to login