Tranona
Well-known member
A smoky old Seagull 40+ (also notionally 55lbs thrust) will comfortably do that It takes very little power to move a slippery boat like that at low speed.
The small ICE outboard.
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B27
Well-known member
40lb of thrust might move a well designed hull at low speed in calm conditions, but it doesn't take much inthe way of wind and waves to overcome 40lb. It will also take a long time to gather speed or to stop the boat.I have had this debate with numerous members at my club, usually while they are swearing and cursing their petrol OB that won't start. They could get a 40lb thrust bison and 50 ah lithium for around £300 which would more than suffice as a shore to yacht motor for their tender.
Ive got a HH27 and would be interested to see how it performs with the 24v Bison (100lb thrust) on an outboard mount. Especially given the feckin issues I am having with the sea water cooling on the Beta 10
A 50Ah LiFePO4 battery probably holds enough energy to meet a lot of what I want from a tender motor, but watch the current rating. Many are internally limited to 50A, so a 50lb trolling motor is typically right at the limit.
I'm hoping my Yamaha will do another few years, so a bigger battery will be affordable.
NickWilson1972
New member
40lb thrust for a small tender would suffice most of the time. A 55lb thrust Bison has pushed my Skipper 14 (70Kg) tender with about 200Kg of crew plus gear at 2.5kts against both wind and tide. Before I went Lithium I got caught out with a lead acid but still found the Bison a useful row assist with it set at low speed (1&2). The LA simply couldn't provide the amps for the higher settings.
B27
Well-known member
If you're claiming 2.5knots over the ground against the tide, that doesn't really mean very much unless you know what the tide was!
If you're claiming 2.5 knots through the water, that doesn't really impress very much.
A Skipper 14 will be less draggy than an inflatable similarly loaded.
Waves slapping on the flat bow of a flubber don't help!
Fair comment that a 100Ah lead-acid battery will be giving a bit less voltage than a 100Ah LifePO4, unless it's fully charged, at 50A discharge.
It should not be a huge difference if the battery is in good nick.
"Suffice most of the time" is a fail.
Adequate power in a tender is a safety issue IMHO.
The tide in many West Country rivers runs quite swiftly.
NickWilson1972
New member
HW +3 Springs. Tide >2kts.
Mudisox
Well-known member
Both my outboards happen to been for servicing/repair and the small rubber dinghy tender has needed oars. Good for the tum. But I use the tide to get to and from the boat. Just take time.
NickWilson1972
New member
Petrol outboards that frequently refuse to restart* is a fail too.
*Carboned up plug, oil in the top end, gummed up carb, dodgy e fuels, moisture in the fuel, Poseidon having a bad day etc etc etc
The issues many people (at my club) have is lugging a 15-20KG outboard to the tender and then from tender to yacht. With petrol outboards all the weight is top end that makes the process more awkward. This is all for a 200-300 metre trip from hard to yacht mooring. For this 2.5-4.5kts is fine.
The trolling motors are in two parts which makes handling easier even if the combined weight is the same or more. with leccy outboards (trolling type) all the weight is bottom end which makes handling easier. . The trolling motors have reverse which is a bonus.
If 40lb thrust doesn't suffice for minimal cost there are 12V 55lb and 68lb versions although a 100ah lithium is more appropriate for these.
Friday I am taking my Hunter Horizon 27 to a Marina (mariner Engineer) as there is an inboard issue. I will sail but will be using a 24V Haswing (which only weighs 6.7Kg) . To be fair I have a 3.5HP Mariner as back up and Im doing this 2 hours either side of HW but will be interesting to see how the HASWING performs with 2 x 100ah lithiums.
B27
Well-known member
At my home port, I don't need an outboard, it's a short row to the boat at high tide, or a walk at low tide.
Where an outboard needs a bit of power is places like Salcombe, the Tamar, the Exe etc, where the water is big enough for some chop to build up and the distance from a mooring to the landing place are great enough that you want to make fair progress.
I've been in these places and found the 2hp barely adequate.
The thing is, the prop on the 2HP is a compromise, so I could be persuaded that 1kW would be OK, but a 'notional' 500W, I don't think so!
This is all just academic for me right now, as the Yamaha shows no signs of dying. Touch Wood!
Where an outboard needs a bit of power is places like Salcombe, the Tamar, the Exe etc, where the water is big enough for some chop to build up and the distance from a mooring to the landing place are great enough that you want to make fair progress.
I've been in these places and found the 2hp barely adequate.
The thing is, the prop on the 2HP is a compromise, so I could be persuaded that 1kW would be OK, but a 'notional' 500W, I don't think so!
This is all just academic for me right now, as the Yamaha shows no signs of dying. Touch Wood!
NickWilson1972
New member
For comparison my Marine 3.5 longshaft pushes the skipper along at 6.5kts. The 55lb thrust (draws about 600w) will push it at 4kts. (in both cases light winds / HW slacks)
B27
Well-known member
Do you actually know it's drawing 600W at 4 knots?
It would be interesting to see these things running with voltmeters and ammeters.
55lb at 4knots would be about 500W of mechanical power. Delivered by the propellor.
NickWilson1972
New member
I have at home in the water butt with a clamp on ammeter plus volt meter. It was drawing 48 amps and 12.3v
590w
efficiency of a brushed motor 70-75%?
B27
Well-known member
Efficiency of a brushed motor could be a bit better than 75% at best.
Efficiency of the propellor is another question though.
Running in a water butt or doing a bollard pull test is not the same load on the prop as pushing a boat at a few knots.
Doing a bollard pull, the prop loads the motor a lot and much current is drawn.
The opposite extreme is driving say a long slim canoe, the motor runs close to its no-load speed, drawing much less current.
Do we assume Bisons and other cheap trolling motors are dumb brushed motors? Even so they some speed control.
My outboard OTOH, is probably a bit over-propped to score its best bollard pull, it won't achieve max engine revs. It will drive a light tender surfing/planing at about 10 knots, so it's perhaps most efficient somewhere around 7 knots. So I can well believe something like a 1kW electric motor could be as good as my 2HP outboard in my 'worst case' use.
Efficiency of the propellor is another question though.
Running in a water butt or doing a bollard pull test is not the same load on the prop as pushing a boat at a few knots.
Doing a bollard pull, the prop loads the motor a lot and much current is drawn.
The opposite extreme is driving say a long slim canoe, the motor runs close to its no-load speed, drawing much less current.
Do we assume Bisons and other cheap trolling motors are dumb brushed motors? Even so they some speed control.
My outboard OTOH, is probably a bit over-propped to score its best bollard pull, it won't achieve max engine revs. It will drive a light tender surfing/planing at about 10 knots, so it's perhaps most efficient somewhere around 7 knots. So I can well believe something like a 1kW electric motor could be as good as my 2HP outboard in my 'worst case' use.
webcraft
Well-known member
Trolling motors are cheap.
Bouba
Well-known member
Yes....but they struggle to make much headway in any sort of chop.
I started with one...and they are great on lakes...but at sea (even a tideless Med) they can suffer. But Porto uses his at sea without issues....so it all depends