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Old 14 May 2013, 12:12   #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, 12:21   #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, 12:24   #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, 12:30   #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, 12:37   #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, 12:44   #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, 12:46   #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, 12:56   #8
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I know it's a bit obvious, but....sail the yacht?
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Old 14 May 2013, 12:58   #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, 13:22   #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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