Towing an Inflatable

RoyS

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Jun 3, 2012
1,739
Hunter 33 Steamboat Wharf, Hull, MA
The other day while sailing and towing our small inflatable it occurred to me that surely the dinghy was slowing us down. I observed our steady speed and wondered what would happen if I cut the dinghy loose. Would we pick up any appreciable speed? As it turned out I was too lazy to perform the experiment but maybe someone here has already done this. How much speed would I gain by leaving the dinghy behind?
 
Oct 22, 2014
20,993
CAL 35 Cruiser #21 moored EVERETT WA
Such an open ended question. What type of dinghy? How heavy? With motor? Etc.
Guessing a knot a knot and a half.
Now the question is what are your sailing plans. Anchor in a sweet little bay? How are you getting to shore for food or exploring?

Only you can judge “should I cut the line and let it drift?”

Inflatable... let the air out and fold it up, tie it up on the bow out of the way till needed.
 
Oct 28, 2013
678
Hunter 20 Lake Monroe
Yes this has been discussed before. I don't know if there is an exact number as to how much it slows you down as there are lots of variables but it does slow you down.

Sam
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Depends.

When there is enough power in the wind or diesel, there is no appreciable decrease in boat speed. For us, in winds above ~12 knots we are already close to hull speed and the dinghy has little or no effect, below 12 knots we may lose up to a half knot or so.

When motoring, we have to increase the power slightly to maintain speed.

Where you tow the dinghy makes a difference. When we can, we try to tow the dinghy on top of the second stern wave. If it is in front of the stern wave, the boat tends to surf down the wave, behind the wave we are dragging it up hill.

The size and type of the dinghy also matters. We have an 8' RIB that tows very nicely and in a straight line, larger heavier boats will require more energy (wind or diesel) to tow. Taking the motor off helps a lot, on our boat it reduces the weight by about 40%. Dinghies that do not track well will slow the boat down more, as they will veer around behind the boat.
 
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Oct 19, 2017
7,732
O'Day 19 Littleton, NH
Dlochner makes a lot of sense. An inflatable rowing dinghy should barely be noticed when set at the right distance behind the boat (top of the second wake). When the dinghy surfs into the trough ahead, she turns at the bottom and loses headway and begins to drift back up the wake to stern until the painter yanks her back around. You can actually feel the sailboat being pulled against, even a larger 56' boat can feel that. Farther back and not only are you dragging the dinghy uphill, but the painter gets buried in the leading wave where it drags and pulls the bow of the dinghy down. Of you don't actually sink the dinghy, it acts like a drogue, plowing deep into the water. Pulling the dinghy up close can work ok, but she may be constantly bumping the transom. I wonder if anyone has experience with a towbar on a dinghy? It can be hard finding just the right balance because wake position will vary with speed and heel. Up close, on a bar, there may be better control over the dinghy with a following sea.

-Will (Dragonfly)
 
Nov 26, 2012
1,653
Hunter 34 Berkeley
Funny you should bring this up. I did that very thing just last weekend. We were sailing down to Half Moon Bay from SF Bay towing our dinghy. We became concerned that we might not arrive before dark so we hauled the dinghy on deck. We picked up about a knot from 4kts to 5kts.
 

capta

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Jun 4, 2009
4,766
Pearson 530 Admiralty Bay, Bequia SVG
Even if it is not about speed, for us it is about securing the most important and expensive bit of boat gear we own. Bringing it aboard takes maybe 5 minutes max, but trying to recover it if it gets loose, flips over or gets run down by some nut job in a high-speed powerboat, will certainly take more time and most likely cost more.
For us, it simply comes down to can we afford to lose our car? Can you?
 
May 7, 2012
1,338
Hunter e33 Maple Bay, BC
How much speed would I gain by leaving the dinghy behind?
No statistical data collected and it certainly depends on conditions such as wave height, wind speed and direction but:
270 Walker Bay inflatable, air floor (69 lbs)
Top of 2nd stern wave
Cruising speed 6.1 kts w/o dinghy, 5.9 kts with dinghy, so approximately 0.2kts slower towing dinghy
Agree with Don S/V ILLusion wrt time, unless sailing across a gnarly body of water.
 
Sep 25, 2008
7,076
Alden 50 Sarasota, Florida
No statistical data collected and it certainly depends on conditions such as wave height, wind speed and direction but:
270 Walker Bay inflatable, air floor (69 lbs)
Top of 2nd stern wave
Cruising speed 6.1 kts w/o dinghy, 5.9 kts with dinghy, so approximately 0.2kts slower towing dinghy
Agree with Don S/V ILLusion wrt time, unless sailing across a gnarly body of water.
That's why God invented davits. :beer:
 
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Bob J.

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Apr 14, 2009
773
Sabre 28 NH
I'm amazed by the amount of people I see towing a dingy with the motor on it. Not sure about other brands but my Achiles owners manual says not to do it.
 
Nov 13, 2013
723
Catalina 34 Tacoma
I have a similar boat size to the OP and to me the loss of speed is a relatively insignificant factor in determining to tow or not. More important are conditions and distance you anticipate towing and if you plan on using it at your destination. Typically it remains on the foredeck inflated. I don't like to inflate more than once a season. My engine is 8hp Tohatsu that weighs 50+ lbs so I only move when necessary. I will tow with engine mounted if conditions are calm but will bungee the motor to it's support so wave action will not cause it to drop down. No fun stopping in a blow to raise the engine. If I'm making a long passage and likely to encounter serious wave action the dinghy and motor are brought aboard. Mounting on it's side on davits would cause the dinghy to drag when under sail (10ft dinghy). Mounting on davits with the dinghy horizontal looks like a great option although for a 33' boat, may be a bit heavy in the stern.
+1 for the top of the second wake.
 

Sailm8

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Feb 21, 2008
1,746
Hunter 29.5 Punta Gorda
You know we are talking about boats that are caught and past by butterflies? A knot or two seems minor in the grand scheme of things.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
You know we are talking about boats that are caught and past by butterflies? A knot or two seems minor in the grand scheme of things.
Well, yes, we have been passed by butterflies and I wish we could out run the biting flies...

A knot or two doesn't sound like much, until you consider that losing 1 knot out of 5 is a 20% drop in speed. That may be nothing on a daysail, however, on a 50 mile leg, it means the difference between a 10 hour trip and and 12.5 hour trip. That's a lot.