Three possible reasons I can think of. My prop is 12x15 so that may be the problem but would I not see some speed increase with more psi and throttle? Another reason may be that 4mph is hull speed for this design. My question is could my rudder which is 1 inch thick and no taper, just a radius create enough drag to slow the boat significantly?
steamboat speed and rudder shape
steamboat speed and rudder shape
Second year with my boat. It is Assassin by Wes Farmer-16 ft. At 50-60psi it run along fine at 4mph. Increasing psi and throttle I still only get 4mph.
Three possible reasons I can think of. My prop is 12x15 so that may be the problem but would I not see some speed increase with more psi and throttle? Another reason may be that 4mph is hull speed for this design. My question is could my rudder which is 1 inch thick and no taper, just a radius create enough drag to slow the boat significantly?
Three possible reasons I can think of. My prop is 12x15 so that may be the problem but would I not see some speed increase with more psi and throttle? Another reason may be that 4mph is hull speed for this design. My question is could my rudder which is 1 inch thick and no taper, just a radius create enough drag to slow the boat significantly?
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Lopez Mike
- Full Steam Ahead
- Posts: 1915
- Joined: Wed Dec 07, 2011 6:41 am
- Boat Name: S.L. Spiffy
- Location: Lopez Island, Washington State, USA
Re: steamboat speed and rudder shape
I suspect that you are up against the traditional 'hull speed' limit set by waterline length. When I try to force my boat beyond that speed I just get a lot of squat and a big stern wave.
As to rudder shape, I just built a new rudder for my new hull and copied a NACA symmetrical shape scaled to about 11% thickness to chord ratio. Mostly set by the thickness of the rudder post. I I did it mostly for esthetic reasons as many boats in my size range have pretty crude shapes. Just slabs of metal welded to the rudder post with no discernible performance loss.
Since I find that I spend much of my steaming time below (well below) hull speed, I've settled on a propeller pitch that yields the least amount of commotion.
Spiffy is 24' overall. Maybe 22' waterline length at moderate speeds. Engine rated at 5 h.p. at 500 r.p.m. and an 18 x 24 prop. Anything much beyond 400 r.p.m. is wasted unless I'm locked into the usual race with my friends! Then it's box full of wood, blower on, draft open and all knobs to eleven.
There is, in case of risk of losing a race, my 2" bore mortar on the foredeck. Take that!
Mike
As to rudder shape, I just built a new rudder for my new hull and copied a NACA symmetrical shape scaled to about 11% thickness to chord ratio. Mostly set by the thickness of the rudder post. I I did it mostly for esthetic reasons as many boats in my size range have pretty crude shapes. Just slabs of metal welded to the rudder post with no discernible performance loss.
Since I find that I spend much of my steaming time below (well below) hull speed, I've settled on a propeller pitch that yields the least amount of commotion.
Spiffy is 24' overall. Maybe 22' waterline length at moderate speeds. Engine rated at 5 h.p. at 500 r.p.m. and an 18 x 24 prop. Anything much beyond 400 r.p.m. is wasted unless I'm locked into the usual race with my friends! Then it's box full of wood, blower on, draft open and all knobs to eleven.
There is, in case of risk of losing a race, my 2" bore mortar on the foredeck. Take that!
Mike
If you think you are too small to make a difference, try sleeping with a mosquito.
Dalai Lama
Dalai Lama
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RNoe
- Full Steam Ahead
- Posts: 257
- Joined: Sun May 26, 2019 5:29 pm
- Boat Name: Cluaran
- Location: Northern Oregon, USA
Re: steamboat speed and rudder shape
Mike:Lopez Mike wrote: ↑Thu Jun 06, 2024 5:12 pm [snip]
There is, in case of risk of losing a race, my 2" bore mortar on the foredeck. Take that!
Mike
As much as I hope to steam our boats together before I croak, remind me never try to race you...
RussN
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RNoe
- Full Steam Ahead
- Posts: 257
- Joined: Sun May 26, 2019 5:29 pm
- Boat Name: Cluaran
- Location: Northern Oregon, USA
Re: steamboat speed and rudder shape
...Although I do wonder what a 5 HP engine and boiler would do in my planing hull...
RussN
RussN
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Lopez Mike
- Full Steam Ahead
- Posts: 1915
- Joined: Wed Dec 07, 2011 6:41 am
- Boat Name: S.L. Spiffy
- Location: Lopez Island, Washington State, USA
Re: steamboat speed and rudder shape
Probably sink it. My boiler alone weighs 400 lbs.
If you think you are too small to make a difference, try sleeping with a mosquito.
Dalai Lama
Dalai Lama
