Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 26-08-2015, 10:59   #16
Registered User

Join Date: Aug 2012
Location: PNW
Boat: Bruce Roberts Ketch 40
Posts: 196
Re: How much does towing a dinghy slow you down

Here is the formula for determining how much drag any object being towed is:

Towing boat displacement - object towed displacement X ( wind speed divided by Hull speed ) + ( Water temperature X 2.76 ) divided by salinity + latitude + 4 X air temperature + -( sea conditions flat 0, following sea + height + speed, choppy head seas spacing / height ratio, ground swells following -3, head +2) = drag of object towed.

Using this formula it will become abundantly clear that:
a) towing a dingy is not a good idea.
b) following these forums can be fun.
__________________

__________________
Maka is offline   Reply With Quote
Old 26-08-2015, 11:12   #17
Marine Service Provider

Join Date: Feb 2012
Location: Vienna, Austria
Boat: Vagabond 47
Posts: 216
Re: How much does towing a dinghy slow you down

Next: I have davits and on short coastal trips I use them but on long distances the dinghy will be on the fore deck, properly fixed.
__________________

__________________
moseriw is offline   Reply With Quote
Old 26-08-2015, 11:32   #18
Senior Cruiser
 
SkiprJohn's Avatar

Cruisers Forum Supporter

Join Date: May 2006
Location: Kea'au, Big Island, Hawaii
Boat: Cascade, Sloop, 42 - "Casual"
Posts: 14,192
Re: How much does towing a dinghy slow you down

Quote:
Originally Posted by Goosebumps View Post
Indeed never tow a dinghy, can easily flip and then serve as sea anchor, also never tow with outboard on for obvious reason that the sea anchor now is even more efficient. An outboard that has been submerged lots of cleaning, greasing, might never wirk properly again.
Yes to this post. It just isn't worth the loss of a dinghy. Once a dinghy is flipped and you are at sea the only way to carry on is cut the painter and let if float away unless you blow some holes in the bottom of the dinghy to release the air pressure holding it inverted. Don't ask me how I know this!
__________________
John
SkiprJohn is offline   Reply With Quote
Old 26-08-2015, 11:40   #19
Registered User

Join Date: Apr 2006
Posts: 4,413
Re: How much does towing a dinghy slow you down

For many they have to do a calculus about what sort of dinghy serves their needs... and if it's RIB for example can it be easily enough stowed on deck or do they need davits... and so on.

A RIB is what works for us... it's not very stowable on the foredeck... and if it is a lot of effort.

We could do davits... I suppose but they are spendy and we still likely need to get the OB off and stow it somewhere... which is now on the rail.

We never tow with the motor on.... the Garhaurer demountable crane works a charm.

And most of our cruising is coastal and sails of no more than 60 miles at a time... so we tow. I would never tow off shore and so the present dink if it can't be stowed would be gone.

Having lived aboard in the Windward Islands for 3 years I realize a good dink is mission critical and I often towed between islands, but didn't have a RIB so at time we hauled in onto the foredeck and lashed it down.

When we go for day sails we leave the dink behind. I love the RIB but don't like to tow... but for me there are no good options.
__________________
Sandero is offline   Reply With Quote
Old 26-08-2015, 12:20   #20
Registered User

Join Date: Sep 2014
Location: Manila, California
Boat: Cape George pilothouse 36 and a Cape Dory 25
Posts: 232
Re: How much does towing a dinghy slow you down

I suspect my 12' x 75 lb. plywood tender does not add too much drag. My evidence is only that as an old man I can row my fully loaded dinghy , exaggeratedly, in circles around a young physically and probably more mentally fit man in an inflatable by himself. We only tow for short hops in protected water though.
__________________
fatherchronica is offline   Reply With Quote
Old 26-08-2015, 12:56   #21
Registered User

Join Date: May 2013
Location: Mangareva, French Polynesia
Boat: Heritage West Indies 36
Posts: 513
Re: How much does towing a dinghy slow you down

Once towed a 12 or 14-foot centre-console with a 70hp motor behind a 55-foot cat all the way from the BVIs to Bermuda. It was fine, but we had a knife strapped next to the cleat it was being towed from and the procedure for if it flipped was to cut the line and let it go. We were prepared to lose the boat. Seas were moderate (had 35 knots for about 24 hours). Towed by a 3-point strop. I'm pretty sure if it had been a single-point tow we would have lost it. Drag was not too bad. We were doing 14-15 knots for a while so the towed boat was planing nicely. I have a video somewhere that i will try to find............
__________________
DefinitelyMe is offline   Reply With Quote
Old 26-08-2015, 15:06   #22
Registered User
 
anacapaisland42's Avatar

Join Date: Aug 2009
Location: Ontario, Canada
Boat: Challenger 32 1974
Posts: 291
Images: 3
Re: How much does towing a dinghy slow you down

Just like towing a picnic table behind you :-)
Bill
__________________
anacapaisland42 is offline   Reply With Quote
Old 26-08-2015, 15:22   #23
Now on the Dark Side: Stink Potter.
 
CSY Man's Avatar

Cruisers Forum Supporter

Join Date: Aug 2003
Location: Ft. Lauderdale
Boat: 2001 Albin 28TE.
Posts: 3,398
Images: 115
Re: How much does towing a dinghy slow you down

As others have said above:
Avoid towing with the motor attached. (Unless short and calm)
Pull the dingy up so it rides on a wake from the big boat, a lot less drag.
Use a proper bridle, not just a painter.

Doing the above, I never had problems.
For Gulf Stream crossings, I always store the dink on the foredeck between mast and stay sail.
(The best compromise, if there is such a thing: a 310 airdeck/air keel Hypalon with a 4 hp/4-stroke Yamaha.. Worked great for me and my CSY 33 Cutter)
__________________
Life is sexually transmitted
www.odincharters.com
www.susanhanssen.com
CSY Man is offline   Reply With Quote
Old 26-08-2015, 15:40   #24
Registered User
 
Hydra's Avatar

Join Date: May 2009
Location: Lorient, Brittany, France
Boat: Gib'Sea 302, 30' - Hydra
Posts: 1,229
Re: How much does towing a dinghy slow you down

Quote:
Originally Posted by Chrisgo View Post
I'm starting to think a rollup with a 2hp motor might be a better option than donating to neptune....
Last month, we found an inflatable dinghy adrift in the mouth of Kenmare River, Republic of Ireland... Both painters had chafed and parted.

Alain
__________________
Hydra is offline   Reply With Quote
Old 26-08-2015, 16:24   #25
Registered User
 
CarinaPDX's Avatar

Join Date: Jan 2010
Location: Portland, Oregon, USA
Boat: 31' Cape George Cutter
Posts: 1,673
Re: How much does towing a dinghy slow you down

I often warn other cruisers about towing dinghies, but it seems most need to lose one first before they accept the advice. My neighbor in Turkey lost his lovely Fatty Knees dinghy by towing it: the afternoon winds/seas picked up, she swamped, the high load broke the painter, and they found they couldn't get back to her. It is an all too common tale. Once the conditions deteriorate it is near-impossible to get the dinghy on deck. Using a triple bridle improves the resistance to chafe, and steadies the dinghy, but once swamped the drag and loads get high.

If the towing boat is fast enough the dinghy will plane and offer very little drag - at least as long as it doesn't get pooped. Otherwise the drag can really cost time on passage. The best thing to do is to make a proper lifting bridle and lay the dinghy down on the foredeck before leaving protected waters, every time. It should only take about 5 minutes to do once the motor is off, and towing with a motor is a fool's errand. I regularly lifted my fiberglass AB RIB onto the foredeck, single-handed - pretty easy to do with a halyard winch, bridle, and a little practice.

Greg
__________________
CarinaPDX is offline   Reply With Quote
Old 26-08-2015, 16:25   #26
Registered User

Join Date: Jan 2008
Location: SF Bay Area (Boat in La Paz)
Boat: Valiant V40
Posts: 432
Re: How much does towing a dinghy slow you down

We used to almost never tow the dink, but as my joints have aged, I'm not quite so adamant.

However, we do still adhere to a few rules:

1. Never on passages
2. Never at night
3. Only weather permitting
4. Almost never with the engine on (once in a great while if calm and short hops)
5. No loose stuff in the dink.

That said, we don't notice too much impact on speed unless in really light airs, maybe 1/2 knot. But, as we tow only during the daytime (and thus shorter distances), the time lost due to towing is partly gained back by the time otherwise needed to stow/relaunch the dink -- even if we leave it inflated on deck.
__________________
jamhass is offline   Reply With Quote
Old 26-08-2015, 17:18   #27
Registered User

Join Date: Aug 2012
Posts: 811
Re: How much does towing a dinghy slow you down

Quote:
Originally Posted by Chrisgo View Post
With a 33 foot boat, displacement 12,000lbs or so, how much would towing an 11' inflatable dingy with 10hp motor slow it down?

In 5 knots of wind I suspect it would be quite draggy - in 10 knots? in 15 knots?

And at what point is it no fun at all dragging a dinghy?
It largely depends on whether you are sailing on the wind or off as well as the sea state. Also if you can adjust the painter so the dinghy is traveling down the displacement wave astern there is a lot less drag than if it is being pulled up the wave. An 11' inflateable with a 10 hip motor is quite a drag. I guess that being 11' it is a RIB which has much less drag than a soft bottom.

I try not to tow my 8'6" RIB dinghy with my 5 hour Mercury attached very often but when I do I tie the motor in the retracted up position to a cleat on either side of the inside of the transom otherwise it swings around on the waves.

I think that the heavier displacement the towing vessel is the less it will be slowed down by the dinghy. It's easier to tow an anchor with a tractor than a bicycle. I would guess that the average speed loss would be close to a knot. Stronger winds probably mean bigger waves and more snatching of the tow rope.

My normal practice is to remove the motor with a purchase on the end of a davit and then lift the dinghy. We sail past most yachts that are towing their dinghies generally speaking. With inflatables you can risk pulling out the metal rings attached to the tubes if you tow with the painter tied to them.

At anchor an inflatable dingy floating astern can flip over in strong winds. One way to avoid that is to take the dinghy painter under the bottom rung of a folded up boarding ladder then up to the deck cleat and pull the dinghy fairly close in.

My davits do double duty as a mount for solar panels. They are also handy as something to hold onto entering or leaving the dinghy. Lift your dinghy if you can, though 11' is quite long and makes a good air brake if it is vertical and risks digging in when you heel if it is horizontal. Not many 33' yachts are 11' across the transom.
__________________
GrahamHO is offline   Reply With Quote
Old 26-08-2015, 17:22   #28
Registered User

Join Date: Aug 2012
Posts: 811
Re: How much does towing a dinghy slow you down

Spell check changed 5 hp Mercury in above post ; to 5 hour Mercury!!
__________________
GrahamHO is offline   Reply With Quote
Old 26-08-2015, 18:53   #29
Registered User
 
Orion Jim's Avatar

Join Date: Dec 2008
Location: Noank, Ct. USA
Boat: Cape Dory 31
Posts: 1,075
Images: 6
Re: How much does towing a dinghy slow you down

Never tow, stow.
__________________
Orion Jim is offline   Reply With Quote
Old 26-08-2015, 19:57   #30
Guy
Registered User

Join Date: Feb 2013
Location: So. Oregon, USA
Boat: Seafarer36c
Posts: 4,308
Re: How much does towing a dinghy slow you down

We towed all last season in Belize. Probably 5 months without bringing it on deck. There was never even close to a problem except I backed over the painter twice, I should say my wife was at the helm one of those times.
__________________

__________________
Guy is offline   Reply With Quote
Reply

Tags
dinghy

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to Slow it Down? Bill Lee Meets & Greets 7 30-12-2009 10:45
Engine Slow = Boat Slow Ex-Calif Propellers & Drive Systems 5 02-10-2007 12:25
Forum slow down... Andy R Forum News & Announcements 18 11-07-2007 16:18
Been there, done that, ready to slow down!!! jjoftheusa Meets & Greets 3 11-11-2003 20:26



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 02:01.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.