Save fuel by following a ferry?

[stuartw]

Recently coming back from Cherbourg by Brittany Ferries, it got me thinking about the enormous amount and waste of energy, spewing out the stern.

Putting on one side safety considerations, I wondered if it was possible to position your boat in the slip stream, and basically catch a flow of water, going in the same direction as the vessel ahead. But whereabouts?. Clearly at the stern, there is vast amount of propeller wash. But is it on the surface, or laminar flow at the depth of the props?

Perhaps the most sensible place is riding behind the bow wave. We do know that migrating geese fly in formation to take advantage of the airflow from the lead goose, and then swap round so they all get a turn. So is this the case from the bow wave of the ferry?
How near to the ferry would you have to go to get the best ride?

Would you have to position you boat ahead of the bow wave or just behind it?

So, are there any hydrodynamicists out there, who may just know the answer?

If the answer is yes, then perhaps the next MBM cruise could go over in a Vee formation – with of course the lead boat being the MBM Broom.

 

[Dave_Snelson]

I reckon you should be able to harpoon a steel hawser over the stern rail (taking care not to kill a passenger on the sun deck!) so that you could, in fact, switch your motors off altogether. And another thing... if you winched said hawser in close to the stern of said ferry, you could catch the sandwiches that are thrown by the kiddies for the seagulls - so you don't even have to pay for lunch.

Oh - and I nearly forgot.. I reckon your chances of a safe passage would be greatly increased by a) the ferry mincing up any of those nasty lobster-pot things before they get to your props and b) in high waves, the ferry just smashes through them, so you get a smooth ride.

There ya go - cheap as chips! /forums/images/graemlins/grin.gif

 

[Gludy]

I have watched dolphins doing this - they seem to glide along without the flick of a tail and they position themselves in fron and behind the bow waves.

 

[BarryH]

I think your missing the point somewhere. The post was refering to the action on the ferry thru the water.
As good as the hawser on the stern rail is, its not very challenging. Personally I'd use the suction zone midway along the ship. Plenty of fenders out and just close in slowly. Let physics and hydrodynamics do the rest. Lot less wear on the cleats and their mountings. No storage of bulky hawsers and launging equip. Almost the same benefits as you method to.

 

[Dave_Snelson]

I have to admit, you seem pretty sharp at this sort of thing Barry!

 

[stuartw]

It's alright Barry, he would have to do that, as there aint too many LPG refuelling stations mid channel, and none when you get to France.

On a slightly more serious note, are you sure there is effectively dead water close to the a big boat? From my observations, there is a lot of disturbed water whipping past, which suggests that water is flowing along the hull.

 

[Wiggo]

Ah, but are they planing or deep keel, SD dolphins?

 

[Bejasus]

I thought they were bilge keeled meself.

 

[Wiggo]

doesn't that big flat tail at teh back make them planing, though? Or do they need bigger engines first?

 

[mcgarry1]

i think if you slapped some nice big sabre 250's on their back they would clear the water quite succesfully, no doubt about it!

 

[Bejasus]

then they would be hydrofoils rather than bige keels.

 

[Gludy]

Dolphins are keeled animals without all your suggestions.. its just that the keel is upside down!

 

[steverow]

Works for caravans travelling in Truck slipstream, about 30 percent less fuel if you can get a good lift down the M5... so why not for boats?

Steve

 

[hlb]

Just dont fancy traveling three feet behind a ferry!! /forums/images/graemlins/shocked.gif

 

[Ifraser]

In my experience of boarding ferries using R.I.B.s I haven't found much slipstream either at the sides or at the stern. I think the only way would be to surf the wake!... Iain

 

[peterandjeanette]

Why not just stow away on the ferry itself. Not so much fun admittedly. But definitely cheaper.

 

[davedpc]

I once followed a ferry back from Calais in heavy headwind /rough sea conditions in my old Cornich Express as far as the Goodwin Sands where we parted company. The ride was tolerable at 15kts and even that we were up and down on the throttles we used less petrol than the trip across from Ramsgate. Dave.

 

[Wiggo]

Why not just pay for a ticket and get on via the gangplank like the rest of us? Cheapskate!