Towing a boat, what speed to use for passage planning?

[fredrussell]

I’m helping a friend move his 31ft, 3 tonne boat, and there’s a possibility I’ll have to tow him with my (identical) boat. My boat has a 30hp engine in good order, and, assuming both boats have a clean hull, I’m wondering what sort of speeds to expect whilst towing? My boat will do just shy of 7 knots flat out under engine, but obviously I don’t want to thrash it. So with my boat doing, say, 2.5k rpm (which would normally give 5.5 - 6 knots) any ideas what I should expect whilst towing?

Obviously there’s loads of variables here, so ball park figures only are sought.

 

[johnalison]

It would help if we knew what waters you are towing in and how far. For a short tow in sheltered water you could work on about five knots but in open water this could be as little as three, or even less.

 

[scozzy]

You say "possibility " so I am assuming his engine is maybe not as reliable as yours?

Another assumption is you are sailing in company as his back up based on above and may not need to tow at all?

Whatever time you have put aside I'd double it and focus on the safe dealing of the many variables as they presented themselves...or not Vs how fast

Good luck

 

[Boathook]

I would half the speed for towing compared to your normal cruising speed. I towed a speedboat in Poole harbour quite a few years back and it made a notable difference on my 4 ton boat with a Honda 30.

 

[Sandy]

I’m helping a friend move his 31ft, 3 tonne boat, and there’s a possibility I’ll have to tow him with my (identical) boat. My boat has a 30hp engine in good order, and, assuming both boats have a clean hull, I’m wondering what sort of speeds to expect whilst towing? My boat will do just shy of 7 knots flat out under engine, but obviously I don’t want to thrash it. So with my boat doing, say, 2.5k rpm (which would normally give 5.5 - 6 knots) any ideas what I should expect whilst towing?

Obviously there’s loads of variables here, so ball park figures only are sought.

Best check your insurance policy before you start. When I was with GJW it forbade it unless it was an emergency.

 

[Tradewinds]

3-4knots will seem plenty fast enough in flat water.

 

[srm]

Depends a lot on the hull form and windage of the vessel being towed. I have found that a small inflatable or rigid dinghy usually reduces speed by around a knot on a very short tow with bow raised, usually slower still on a longer tow rope. Towing a trad wood 18 ft double ender on a long tow took me down to about half normal cruising speed. Then even slower when the head wind got up. Towing vessel was a displacement yacht about 8 tons and inboard diesel.

Be very careful in a following wind and sea as the tow on a long rope can run up into your stern.

 

[Refueler]

I’m helping a friend move his 31ft, 3 tonne boat, and there’s a possibility I’ll have to tow him with my (identical) boat. My boat has a 30hp engine in good order, and, assuming both boats have a clean hull, I’m wondering what sort of speeds to expect whilst towing? My boat will do just shy of 7 knots flat out under engine, but obviously I don’t want to thrash it. So with my boat doing, say, 2.5k rpm (which would normally give 5.5 - 6 knots) any ideas what I should expect whilst towing?

Obviously there’s loads of variables here, so ball park figures only are sought.

Surprisingly - the speed will often build up during a tow - unless you have waves / swell cutting you back.

I've towed many with my 25ft'r as it has 43HP .... at cruise she makes about 5kts ..... with a tow ... I've towed similar size weight (4 tons) and speed dropped to about 4kts after it had crept up over time from the initial 2.5 - 3kts.

The main point when towing is to have regard to the fittings tow line is made off to. I use a Y bridle on my boat - so both aft cleats take the strain. I've seen some people have a sliding bridle ... NO WAY !! I fix the tow to be dead centre of the bridle.
On the boat being towed - I lead to stemhead and then back up the tow line with a U line ... each arm of U going down side decks to aft or midships cleats to back-up and help take strain.

No need for snubbers or other paraphernalia ... as long as tow is reasonable length - that will have enough cushion effect.....

Here's my towing a boat albeit small in Sweden for near half day ....

Guy reckoned I towed him faster than he usually sails !!

 

[Corribee Boy]

I misunderstood the thread title at first... I was going to say, I usually aim for about 60mph around the M25 with the Corribee on its trailer behind the Landrover...

 

[Refueler]

I misunderstood the thread title at first... I was going to say, I usually aim for about 60mph around the M25 with the Corribee on its trailer behind the Landrover...

I nearly got caught speeding with my Alacrity behind my Capri 2.8i !!

 

[MontyMariner]

a possibility I’ll have to tow him with my (identical) boat.

Is the possibility of sailing also ruled out?

 

[Refueler]

I would half the speed for towing compared to your normal cruising speed. I towed a speedboat in Poole harbour quite a few years back and it made a notable difference on my 4 ton boat with a Honda 30.

The strange thing is the boat towing and boat towed ... the type of boat can make a huge effect on the tow .....

A McGrgegor 26 with 50HP on back could not tow my 25ft 4 ton boat when we grounded ... she was in light mud only ... the M26 skidded about like a drunken sailor ... just could not 'bite' .... such that I asked owner to ferry my people ashore and leave me on board.
Once he was clear - with anchor and genny - I got her free, and back up to HYCO .....

I have towed pontoons with my Soviet era speedboat ... again - the lack of bite ... but successful. With my 25ft'r - the tow was completely different and felt so controlled ...

 

[fredrussell]

Thanks for all responses. The boat being towed will be fine to sail, but if the wind drops a lot the engine is a bit of an unknown. He’s just bought the boat and it’s sat for a fair while. We’ll rig up a temporary fuel tank with fresh diesel, and engine has had a good service since purchase.

 

[Refueler]

Thanks for all responses. The boat being towed will be fine to sail, but if the wind drops a lot the engine is a bit of an unknown. He’s just bought the boat and it’s sat for a fair while. We’ll rig up a temporary fuel tank with fresh diesel, and engine has had a good service since purchase.

Sail in company ... have a light line ready to throw over to start the process of hooking up ....

I put a $ down that you guys make it without any fuss !

 

[Porthandbuoy]

I'd expect around half of your usual cruising speed, but build the speed up slowly.
Don't want to teach you to suck eggs, but make sure you use a stretchy warp for towing. eg. Anchorplait, Octoplait or basic 3-strand Nylon. Polypropylene is another option as it floats and you're less likely to wrap it around your prop if the tow goes slack. Use an old sheet rope or halyard and you'll almost certainly rip a cleat out.

 

[Refueler]

I'd expect around half of your usual cruising speed, but build the speed up slowly.
Don't want to teach you to suck eggs, but make sure you use a stretchy warp for towing. eg. Anchorplait, Octoplait or basic 3-strand Nylon. Polypropylene is another option as it floats and you're less likely to wrap it around your prop if the tow goes slack. Use an old sheet rope or halyard and you'll almost certainly rip a cleat out.

Read my post ....... #8 ..... and you'll not rip a cleat out ...

Towed boats many times over many years in and outside harbour waters ....

 

[bikedaft]

Read my post ....... #8 ..... and you'll not rip a cleat out ...

Towed boats many times over many years in and outside harbour waters ....

Pretty sure he meant you would rip a cleat out if you used e.g. a halyard rather than stretchy rope.

 

[jdc]

The attached graph is for my boat, so yours will be a bit different but the principle applies: you will have twice the resistance, so see what reduction in speed you can expect. So in my case, if I motor at 6kts normally (at x rpm) which is a drag of 1000 Newtons. 500N is at 4.5kts which gives the speed with both boats at x rpm. Not an exact calculation, but a reasonable approximation. Better than a hand waving 'allow half the speed'.

 

[Refueler]

Pretty sure he meant you would rip a cleat out if you used e.g. a halyard rather than stretchy rope.

If the scope is sufficient - you can use any rope you like ...... ever tried the rope and paper trick ?

Get two people and a length of any rope you like ... fold a piece of paper at mid point ..... now try get those people to get that rope straight by pulling ends ... its impossible.

The scope of rope gives you the 'snatch' elasticity ....

Look upon it this way - commercial towing using chain and wire hawser - not only for strength - but also for that catenary effect ...

Blimey ... c'mon guys ..... decent tow line ... bridle to spread load .... sort how to make fast to boat to tow ... see post #8 .....

 

[Refueler]

The attached graph is for my boat, so yours will be a bit different but the principle applies: you will have twice the resistance, so see what reduction in speed you can expect. So in my case, if I motor at 6kts normally (at x rpm) which is a drag of 1000 Newtons. 500N is at 4.5kts which gives the speed with both boats at x rpm. Not an exact calculation, but a reasonable approximation. Better than a hand waving 'allow half the speed'.



View attachment 168288

Sorry but theory and practice ??

Once a tow is underway - the speed can actually creep up over time to a reasonable % of usual speed .... done it - got the T shirt ... without need of fancy theory tables / graphs ...