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Old 14 May 2013, 11:12   #1
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Towing behind a RIB

I'm doing a sailing event in the summer and we're planning to tow the boat from Hamble to Cowes behind our 5.2m Valiant rib, provided it's not too rough.

The rib has a 75hp 2 stroke Mariner engine on the back, and it usually drinks about 12 litres of fuel getting across the Solent to the IOW.

The boat we're going to be towing is about 8 metres long and weighs about 1500kg. It will start planing if we tow it at 10 knots or faster.

So my question is, how much fuel should we expect to use and would do you reckon the most fuel efficient speed to tow the boat at is? We've got a 25 litre tank but we don't really want to get halfway across the Solent and run out of juice. Thanks guys.
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Old 14 May 2013, 11:21   #2
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You need at least 50 litres.
You'll need to lash up alongside and to the stern rather than tow.
And don't plane.
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Old 14 May 2013, 11:24   #3
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You'll need to lash up alongside and to the stern rather than tow.
You do when taking out to sea and when moving around at berth but I'd be happy on a tow astern when crossing the open water.
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Old 14 May 2013, 11:30   #4
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Just thinking about controlling a stop or turn on a busy waterway and then the control in Cowes. No mention of whether the sailer has an engine.
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Old 14 May 2013, 11:37   #5
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Just thinking about controlling a stop or turn on a busy waterway and then the control in Cowes. No mention of whether the sailer has an engine.
The boat will come out of the marina and out of Hamble under it's own steam, and it will motor into the marina in Cowes itself too. I'd imagine we'll be fine once in open water, we've got people with us who know the Solent extremely well and have a lot of experience so we should be okay in that respect. It's a very light boat for it's size so as soon as you take the power off the RIB the boat will slow right down pretty quickly.

We just don't really fancy motoring all the way to Cowes with a piddly little 2hp engine. Even if the water is perfectly flat it will take literally hours. We've done it before and it was an absolute nightmare, we simply haven't got the time this time round.
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Old 14 May 2013, 11:44   #6
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The boat will come out of the marina and out of Hamble under it's own steam, and it will motor into the marina in Cowes itself too. .
Don't blame you 2hp would be nasty. I'd be going for astern tow
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Old 14 May 2013, 11:46   #7
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Should be fine then, keep the weight on the sail boat well back.
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Old 14 May 2013, 11:56   #8
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I know it's a bit obvious, but....sail the yacht?
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Old 14 May 2013, 11:58   #9
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I wouldn't think you will get a 1500 KG sailer planing behind the RIB. Personally I would tow it astern and vary your line length to try and match wave sets. I find when towing dinghies in that it devours fuel big time, especially if I am trying to coax 6 or 8 lasers to get up to 8-10 knots with my 140 Suzuki 2 stroke. I find there is a hump which is difficult to get over when towing. The RIB doesn't really start planing until 14 knots. Towing up to 6 or so isn't too bad. Trying to get up to 14 requires a lot of power to achieve very little and I can see the fuel gauge moving. I don't bother going for the faster speeds now, it is better to travel at what is comfortable and save the fuel. Is it a keel boat? Will you have someone steering it?
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Old 14 May 2013, 12:22   #10
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Originally Posted by treerat View Post
Don't blame you 2hp would be nasty. I'd be going for astern tow
Awesome, thanks for the advice.

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Should be fine then, keep the weight on the sail boat well back.
Will do, thanks very much.

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I know it's a bit obvious, but....sail the yacht?
We could do but there's only a very small wind range where that's really feasible. It's quite a sporty boat, if there's any real wind you need the weight of a full crew or it's very wet and slow. Plus we're going to have brand new sails for the event and we don't want to waste them on a delivery trip because they really don't last very long.

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I wouldn't think you will get a 1500 KG sailer planing behind the RIB. Personally I would tow it astern and vary your line length to try and match wave sets. I find when towing dinghies in that it devours fuel big time, especially if I am trying to coax 6 or 8 lasers to get up to 8-10 knots with my 140 Suzuki 2 stroke. I find there is a hump which is difficult to get over when towing. The RIB doesn't really start planing until 14 knots. Towing up to 6 or so isn't too bad. Trying to get up to 14 requires a lot of power to achieve very little and I can see the fuel gauge moving. I don't bother going for the faster speeds now, it is better to travel at what is comfortable and save the fuel. Is it a keel boat? Will you have someone steering it?
Yeah I can imagine it's quite hard work for the RIB. Maybe we won't be going for planing speeds then. We definitely want to go for fuel efficiency rather than speed, as long as it gets the boat there faster than the 2hp we'll be happy. Yeah, it's a small keelboat. I think someone will need to steer it yeah, otherwise the rudder will be flapping about all over the place.
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Old 14 May 2013, 13:49   #11
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I was in a rib when we towed a 1720 across from pwllheli to abersoch behind a 5mt humber with a 60hp, that got on the plane and was fine, but then it was suited for it! Just get a long stretchy rope and plan for the weather.
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Old 14 May 2013, 14:25   #12
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Lash the helm on the sailboat. Have an adjustable to tow line so you can try to match the wave sets; I wouldn't plan on planing anything.
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Old 14 May 2013, 16:42   #13
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And don't tow alongside!! You will be slower, wetter, use more fuel and add to wear and tear on both boats....
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Old 15 May 2013, 02:27   #14
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When you start to get into to the confines of a harbour or it starts to get busy with other boats & you don't want to lash alongside
towing a drouge or an old car tyre on a short line behind the sailing boat helps stop the it from overtaking you or crashing into the back of your own boat if you have to stop or slow down quick
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Old 15 May 2013, 03:14   #15
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Definitely tow! Motored an SB3 from hamble to Cowes for the RTI race. It took an incredibly longtime!
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Old 15 May 2013, 03:39   #16
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Silly Q - what speed does the yacht start to plane at? I've towed 420s on the plane with the SR4 still digging holes in the water....

Personally I'd rather have someone aboard the yacht on the helm - that way if it does overtake you can guarantee it will miss you!
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Old 15 May 2013, 04:01   #17
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the one thing to watch out for is the plugs oiling up, not sure how suceptable the mariners are to that but lots of medium/low revs running might clog them up a bit.
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Old 15 May 2013, 04:59   #18
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Lash the helm on the sailboat. Have an adjustable to tow line so you can try to match the wave sets; I wouldn't plan on planing anything.
I'd much rather have someone steering the yacht, I think it'll be much safer that way if something goes wrong. I'm planning to take the line through a cleat and onto a winch onboard the yacht so we can adjust the length of the tow.

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And don't tow alongside!! You will be slower, wetter, use more fuel and add to wear and tear on both boats....
That's what I thought would happen, I can just imagine big jets of water shooting up between the two boats. :S It'll only come alongside when we're switching people between the boats and getting the boat through tricky spaces etc.

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When you start to get into to the confines of a harbour or it starts to get busy with other boats & you don't want to lash alongside
towing a drouge or an old car tyre on a short line behind the sailing boat helps stop the it from overtaking you or crashing into the back of your own boat if you have to stop or slow down quick
Ah thank you for the tip. I'll try and get hold of something like that, although I imagine we'll have to take the boat alongside so we can get someone onboard to get docklines out etc.

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Definitely tow! Motored an SB3 from hamble to Cowes for the RTI race. It took an incredibly longtime!
On an SB3 that must have been horrendous! Our boat is bigger and a bit more enclosed than an SB and it's still not fun.

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Silly Q - what speed does the yacht start to plane at? I've towed 420s on the plane with the SR4 still digging holes in the water....

Personally I'd rather have someone aboard the yacht on the helm - that way if it does overtake you can guarantee it will miss you!
It will get up on the plane at around 10 knots of boatspeed, it'll happily surf down any waves there are too. We don't have to tow it that fast but I just thought that getting the boat on the plane would reduce the loads in everything etc. I think having someone steering is the best way to do it, really don't fancy running it up the RIB's backside!

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the one thing to watch out for is the plugs oiling up, not sure how suceptable the mariners are to that but lots of medium/low revs running might clog them up a bit.
Oh I hadn't thought of that. Thanks for the warning! I'll talk to the guy who looks after the engine for us and see if he thinks it'll be a problem.
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Old 15 May 2013, 05:07   #19
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Towed a 1720 from Kip to Tarbert a few years ago, we averaged around 12 knots with the 1720 being towed astern, it was no bother at all. Cant remember exactly how much fuewas used, I do remember being surprised that I hadn't used more.
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Old 15 May 2013, 08:34   #20
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Thing with yachts is they are designed to either slip through the water with minimal resistance or skite across the top.....

Yonks ago I once towed some ridiculous tonnage of classic 8m into Rhu from the patch with a 25 on an SR4. Took lots of throttle and f-o-r-e-v-e-r to get moving, but once on the go I throttled back & let momentum do it's thing.
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