Rocker Bottoms

[rebar]

The shape is efficient enough for a powered hull, but you mention rowing. If you are going to spend a significant amount of time rowing, the flat stern will be very "draggy", and slow you down.
Its a function of how much time you expect to be travelling over say 8-12 knots.

Skip Johnson recommended that if I build the stern like the bow for less drag, he would "recommend doing about half the front rocker as a compromise." But how would I build a 10 hp out board mount on a raked stern?

I will have to row 10 miles on my first journey bc its in the Bridger Wilderness area, but I would like the option to row and explore other no motor area's and be able to float and maneuver shallow rivers.

 

[Skip Johnson]

Is there any "white water" in your projected use? Like more than class 1 rapids. My mental image of your use is leaning towards a really low freeboard platform like the love child of a barge and a sit on top kayak. Stand up face forward rowing comes to mind and if you're happy with 4 mph piddling along instead of rushing to some destination cobble up a small stern paddle wheel for use where motors are allowed, even in really shallow water.

 

[rebar]

No white water Skip, but i could see having to drag it over shallow riffles here and there. Riffles would tear anything other than oars up. I initially thought I would sit on-top of the barge to row, and why I reduced the free board. But I'm leaning toward the 24" free board and rowing from inside. For my 20x7 with a 1-inch draft and a 10-inch seat height, I need total oar length of 9.5'and oar port height of 11 " up from the bottom of the boat.

 

[portacruise]

A flexible trailing shaft motor might be used to power up or down shallow and riffles if there is 3-4" of water to work with, where paddles/oars/push poles/dragging won't work. Motor works so long as the bottom surface is sandy or small movable pebbles, but it won't work if there is medium or large rocks/ boulders anchored and blocking. My 1 man boat is light enough to carry with backstraps and portage around significant blockages, so long as I can crawl over instead of dragging. This link at post #8 shows how the propulsion idea works; prop kicks upward, slides through and goes to surface piercing with whatever depth of water remains:

P

Post in thread 'Propeller position for optimal water flow'

Oct 7, 2025

Here's the general idea, but it is more efficient without the encased cover on a flexible trailing shaft, and the bare shaft will curve while exerting propelling Force so that the prop aligns to the horizontal constantly to the flow of water, once a certain minimum of force is applied.

1/16 inch spring steel bare for the 600mm boat length shaft, Maybe 75% the boat length, or longer, depending upon how much force is being exerted by the motor. The flexible shaft remains straight below some minimum force but Bends to the horizontal once over that minimum force. The design...

• portacruise

• 

There are much larger commercial versions, some are called mud motors..

 

[rebar]

Is there any "white water" in your projected use? Like more than class 1 rapids. My mental image of your use is leaning towards a really low freeboard platform like the love child of a barge and a sit on top kayak. Stand up face forward rowing comes to mind and if you're happy with 4 mph piddling along instead of rushing to some destination cobble up a small stern paddle wheel for use where motors are allowed, even in really shallow water.

I should have mentioned that if white water is presented, I usually shoot them.. Like when I shot multiple rapids instead of portaging my loaded two man lake kayak up in the MN boundary waters alone.. And another time I took the same two man lake kayak down the CO Taylor and Gunnison alone.. What a ride..

 

[rebar]

A flexible trailing shaft motor might be used to power up or down shallow and riffles if there is 3-4" of water to work with, where paddles/oars/push poles/dragging won't work. Motor works so long as the bottom surface is sandy or small movable pebbles, but it won't work if there is medium or large rocks/ boulders anchored and blocking. My 1 man boat is light enough to carry with backstraps and portage around significant blockages, so long as I can crawl over instead of dragging. This link at post #8 shows how the propulsion idea works; prop kicks upward, slides through and goes to surface piercing with whatever depth of water remains:

P

Post in thread 'Propeller position for optimal water flow'

Oct 7, 2025

Here's the general idea, but it is more efficient without the encased cover on a flexible trailing shaft, and the bare shaft will curve while exerting propelling Force so that the prop aligns to the horizontal constantly to the flow of water, once a certain minimum of force is applied.

1/16 inch spring steel bare for the 600mm boat length shaft, Maybe 75% the boat length, or longer, depending upon how much force is being exerted by the motor. The flexible shaft remains straight below some minimum force but Bends to the horizontal once over that minimum force. The design...

• portacruise

• 

There are much larger commercial versions, some are called mud motors..

Neat.. Thanks.

I'm looking at a IP68 submersible motor swinging a 10" surface piercing prop. I would have to water cool the motor if I used it inboard so I want to build a steerable transom mount and play with depth, instead of spending 15k on a electric outboard. But I'm still playing with the idea of inboard so that long-tail mud motor could work.

 

[portacruise]

Submersible motors usually don't play well with shallow water hitting bottom or rock collisions (got stranded once). Also, if there is possible weed or fishing line entanglement, it might be necessary to jump out and go underneath to clear the prop. There usually isn't time to manually pull up or tilt up a troll motor, it's especially bad if the water is stained, can't see it coming. Many years ago I was able to easily make my own long tail using a cheap surplus motor (no cooling) with a cheap Asian long tail motor kit that came with mounting platform and everything else except the motor. But I don't know if still a company that still sells the kit separately in the USA.

 

[rebar]

Thanks. I found this 20 hp electric long tail which isn't designed for open water. It would cost me an extra $7,600 compared to the 17 hp Reacher Tech D70L165 I've been eyeing. On the other hand, the electric long tail is proven turn key but with the Reacher, I'm still looking at building the steerable outboard bracket to position the motor..

 

[portacruise]

Thanks for the link, those were not available many years ago when I made mine. Amazon has a 15hp petrol for under $600, Ebay about 50% less. Long tails generally don't have a reverse and don't steer well for more than a few feet when run in reverse.

I also like to shoot rapids that are safe for my tiny boat. So I always go against the forces first, upstream for rivers or upwind on lakes. That allow me to coast back to launch point with a paddle steering in case of emergency. Also going up allows scouting/walking the shallow water and rapids hazards coming back down. That way, I can carefully plan my path or alternatives if it is too rough, shooting down.

 

[rwatson]

But how would I build a 10 hp out board mount on a raked stern?

Huh? You just need the stern rocker to curve up until water level is reached. Everything above that can be vertical, for mounting an outboard.