How much drag would you say an 8’ inflatable being towed at 4 knots creates? There is quite a bit of tension on the tow line at this speed. Would it take off as much as a knot ,or more like 1/4 or a 1/2 knot?
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Drag weight
When towing your dink, does it have a small outboard on the transome?
I tow a 9'9" Titan with an inflatable keel so it tracks quite well but with a 60# 5HP honda on the transome combined with the 80# dink I am hauling some serious weight. I am not sure how many knots I lose but I do know it takes me an extra 300 -500 RPM to maintain the same speed as the same boat running beside me that is not towing. (two MacGregors w/50HP honda)
Another thing I have discovered is that every other sailboat passes me when we are all under sail when I tow, the dink really drags my a$$.
When towing your dink, does it have a small outboard on the transome?
I tow a 9'9" Titan with an inflatable keel so it tracks quite well but with a 60# 5HP honda on the transome combined with the 80# dink I am hauling some serious weight. I am not sure how many knots I lose but I do know it takes me an extra 300 -500 RPM to maintain the same speed as the same boat running beside me that is not towing. (two MacGregors w/50HP honda)
Another thing I have discovered is that every other sailboat passes me when we are all under sail when I tow, the dink really drags my a$$.
It depends on the dinghy... inflatables tend to create more drag than rigid hull dinghies... I also highly recommend you remove the dinghy outboard from the dinghy before trying to tow it. If the dinghy flips or swamps, you could seriously damage the outboard by submersing it.
BTW, shouldn't post multiple threads on the same subject...
Not good net etiquette.
BTW, shouldn't post multiple threads on the same subject...
Not good net etiquette.
Are you towing the dingy so it's surfing the wake, climbing the wake, or beyond the swell. I've tried different positions and notice a different feel to the line. A spring scale would probably give you some sort of idea of the tension, but I don't know how you would translate that into drag. I tow my inflatable without motor mounted for conveniece and it's a good trash hauler.
All U Get
All U Get
I have a 11' inflatable with an outboard attached but not in the water. Depending on where I have it set behind the boat can cost me anywhere from almost nothing to 1 knot of speed. I find the best spot is in the trough of the first wake off the stern. It rides the wake, yet remains in control. Actually it rides more stable than if I forget and set it too close to the boat.
As for having the motor on while towing being a bad idea, I don't disagree and accept the risks. The issue lies with the weight of the 8hp motor. It's just a bit too heavy to lift on and off from the swim platform. Some day I'll opt for a lifting arm to solve the problem. In the interim I've found that in rough weather setting the motor so it's riding in the water creates more drag, but that same drag helps to stabilize it.
As for having the motor on while towing being a bad idea, I don't disagree and accept the risks. The issue lies with the weight of the 8hp motor. It's just a bit too heavy to lift on and off from the swim platform. Some day I'll opt for a lifting arm to solve the problem. In the interim I've found that in rough weather setting the motor so it's riding in the water creates more drag, but that same drag helps to stabilize it.
Re: hard tender
I think that a lot of these questions can be answered with a spring scale and an adjustable painter on the dink. Tow the dink at various speeds and distances from the mother boat and record the boat speed and the load on the scale. Then with someone in the dink tow it at speed and set it adrift and note the speed change. Then don't forget to go back for the dink and its crew. ;D
I think that a lot of these questions can be answered with a spring scale and an adjustable painter on the dink. Tow the dink at various speeds and distances from the mother boat and record the boat speed and the load on the scale. Then with someone in the dink tow it at speed and set it adrift and note the speed change. Then don't forget to go back for the dink and its crew. ;D
But the extra person in the dink will affect the drag. You need a shadow boat to pick up the dink when it goes adrift.
Sounds like a great research article for one of the sailing mags.
Re: hard tender
Ross, the first part of your suggestion is great. But why do you need a spring scale or someone in the dink? I'd bet most people already know how fast they run through the water without towing anything. Tow the dink, try adjusting it in relationship to your wake and note the speed change. The math should be simple. With the time you save hooking up a scale you can knock back a cold one or two.
Mike
Ross, the first part of your suggestion is great. But why do you need a spring scale or someone in the dink? I'd bet most people already know how fast they run through the water without towing anything. Tow the dink, try adjusting it in relationship to your wake and note the speed change. The math should be simple. With the time you save hooking up a scale you can knock back a cold one or two.
Mike
I'm with you Ross using a fish scale would give you empirical information. I tried changing the length of the painter on my way back from Catalina last summer and could not find a spot that I could discern by touch that had the least pull.
I tried changing the lengths of the bridals to see if I could get it to move sideways to surf the wake, to no avail. I couldn't find a second wake at 4 kts.
I do know that with the motor idling and in a light wind I can easily hit 6.4 kts but with the dink 4 was the best I could do. The pull was more than I could handle with out a winch.
Frank
I tried changing the lengths of the bridals to see if I could get it to move sideways to surf the wake, to no avail. I couldn't find a second wake at 4 kts.
I do know that with the motor idling and in a light wind I can easily hit 6.4 kts but with the dink 4 was the best I could do. The pull was more than I could handle with out a winch.
Frank
Thanks
Thanks for insight into speed reduction. Ours does not have a keel and we do leave a 20lb electric motor on it. Drag was only mentioned as it would relate to speed. A change of 300 to 500 rpm is not insignificant nor is 6.4 to 4 knots or nothing to 1 knot, so towing clearly makes a difference in speed. Next season we will experiment with tow distance, to have it ride in the best spot, it looks like this makes a big difference.
The double post was a mistake. I posted once, then after a few minutes or so checked recent 1-day activity. Nothing .So I did it again with another browser and still nothing, so I gave up and came back later still nothing, so I checked 2 day activity and both showed up.
Thanks for insight into speed reduction. Ours does not have a keel and we do leave a 20lb electric motor on it. Drag was only mentioned as it would relate to speed. A change of 300 to 500 rpm is not insignificant nor is 6.4 to 4 knots or nothing to 1 knot, so towing clearly makes a difference in speed. Next season we will experiment with tow distance, to have it ride in the best spot, it looks like this makes a big difference.
The double post was a mistake. I posted once, then after a few minutes or so checked recent 1-day activity. Nothing .So I did it again with another browser and still nothing, so I gave up and came back later still nothing, so I checked 2 day activity and both showed up.
One other point... if you're towing a dinghy in any sort of sea... having the dinghy a wave length behind the mother ship is a good idea... that way it won't surf down into the back of the mother ship or tug at the painter as much.
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