Towing 5.8m RIB with 2014 DF115 behind larger boat on bridle. Motor up or down?

 

 
Hi everyone,

For the past year I have towed the RIB on bridle with the motor down. Recently a friend with a brand new Mercury motor has had warranty made void because of towing with the motor down causing the motor to hydraulic by forcing water back up through the exhaust. Can anyone advise if this is possible with the DF115 and should I be towing with the motor up? I was always told to keep it down for stability and tracking purposes. I usually tow the RIB at around 16 knots.
I appreciate your advice.
Thanks
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ROUGH RED

One day I hope to replace the boat picture I am using with one of a decent fish...One day...


ranmar850's picture

Posts: 2266

Date Joined: 12/08/12

Up, for mine

Tue, 2019-03-05 12:24

 Don't know about the hydraulic, but it will obviously cause the prop to windmill furiously. .I  have always towed with motor up,  allowing the towed hull to run naturally through the water. My worry with towing with it down would be self steering, if the steering went off centre, real risk of having the towed vessel roll over. I know that the water pressure on the leg "should" keep it centred, but....

Escape's picture

Posts: 76

Date Joined: 14/12/11

Up for mine

Tue, 2019-03-05 13:58

 Thanks ranmar850,

You make a good point. So far....... the issue of steering going off centre hasnt been a problem, (hydraulic steering) but if it did I can imagine the problem. The RIB to date has towed dead straight. I guess one benefit of the motor up would be reduced drag on the towing boat. 

Cheers.

Anybody else experienced the hydraulic issue?

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ROUGH RED

One day I hope to replace the boat picture I am using with one of a decent fish...One day...

Lavs's picture

Posts: 144

Date Joined: 30/04/12

 Think the mechanic was

Wed, 2019-03-06 22:54

 Think the mechanic was probably meaning hydro-lock, not hydraulic. Water through the exhaust port and into the cylinder via the exhaust valve. Water won’t compress when the piston goes up so it locks the engine up - worst case breaks a con rod. 

Never thought about it happening due to towing with the outboard down - good info. 

Escape's picture

Posts: 76

Date Joined: 14/12/11

 

Thu, 2019-03-07 09:43

 

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ROUGH RED

One day I hope to replace the boat picture I am using with one of a decent fish...One day...

scubafish's picture

Posts: 608

Date Joined: 15/08/12

UP.

Tue, 2019-03-05 16:40

 ,

Small rib (rigid inflatable ) had a steer lock on it and we would lock that off and leave the leg down and in gear for small travel distances.Would keep the boat straight and keep a bit of tension on the tow line.(12ft rib/47ft boat)

But a boat that size put the motor up on the boat being towed and tow it from the winch point .also distance from the towing vessel i think should be about the back of  third wave back from the boat.Too long it will wander too short very dangerous. 

If your being towed by a charter boat "SKIPPERS CALL OF THE CHARTER BOAT".

https://www.whitworths.com.au/3-strand-polyester-mooring-rope

Tip:

1: splice all loops and back splice ends.

2: Bridle needs to be strong enough to tow from one point in a turn(port or starboard)

3:Make sure the skipper knows whats going on when shortening up a tow line,fingers can be lost and deckys can end up over the side if he puts on the power and your still holding the tow line and keep your feet out of and away from the incoming line"DECKY NEEDS TO YELL OUT TOW LINE SECURE" before he takes off. 

4: Secure all goods on the towed boat and centre and secure all weight.Large weighted items should be removed to lighten the load.

That's all I think.

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Escape's picture

Posts: 76

Date Joined: 14/12/11

 Thanks Scubafish,Looks like

Tue, 2019-03-05 16:41

 Thanks Scubafish,

Looks like up it is.

I am happy with the bridle set up / distance from stern of towing boat to RIB - and yes I secure the bridle to the winch point on RIB and bridle on towing boat is a "Y"  with float coming from both rear points on towing boat.

The decky / skipper communication is as you say critical when letting the RIB out from being on short rope and just as critical bringing it back in alongside to a short rope when entering the marina or Thompsons Bay.

Appreciate your post.

Thank you.

____________________________________________________________________________

ROUGH RED

One day I hope to replace the boat picture I am using with one of a decent fish...One day...

scubafish's picture

Posts: 608

Date Joined: 15/08/12

Also

Tue, 2019-03-05 16:46

Small children need to stay in the cabin when dealing with ropes on a deck,my daughter nearly got riped over the side one day as she was standing on a towline when it was let go.

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Escape's picture

Posts: 76

Date Joined: 14/12/11

Safety First

Tue, 2019-03-05 16:49

 Yep, it should be enjoyable, not an extreme sport.

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ROUGH RED

One day I hope to replace the boat picture I am using with one of a decent fish...One day...

carnarvonite's picture

Posts: 7822

Date Joined: 24/07/07

Interesting

Thu, 2019-03-07 06:55

 Interesting to hear of the warranty claim, have towed literally hundreds of boats in at speeds of up to 20+ knots without anyone coming back to us at sea rescue with a report of hydraulicing . 

 

We usually tow with motor down if people on the boat and motor up if vessel is empty due to weight distribution and someone moving about in the towed vessel and tow from from the trailer eye not the samson post to keep the nose up. With a following sea it pays to hang a small drogue off the stern of the towed vessel to stop it surfing and possibly broaching.

 

On the hydraulicing, the only reports I have heard of this is from crews practicing emergency stops in higher speed vessels causing water to be forced back up the exhausts virtually demolishing the engines. A report was issued to all groups warning of this practice and advising to stop doing it.

Escape's picture

Posts: 76

Date Joined: 14/12/11

 Thanks Carnarvonite,I can

Thu, 2019-03-07 09:46

 Thanks Carnarvonite,

I can certainly understand the emergency stop scenario.

looks like we all learn something new every day.

 

Cheers.

____________________________________________________________________________

ROUGH RED

One day I hope to replace the boat picture I am using with one of a decent fish...One day...