|
|
14 November 2016, 16:10
|
#1
|
Member
Country: UK - England
Town: Newquay
Boat name: Shelly
Make: nawhal
Length: 5m +
Engine: 75
Join Date: Nov 2016
Posts: 13
|
High speed 'wobble'
Hi all, I've just got a Narwhal 4.8M rib with a Mercury 75hp 2 stroke - all in great shape and well maintained. At above 20 knotts with the engine trimmed slightly up she can start to 'weave' slightly from side to side feeling like she is tipping slightly from one side to the other. trimming the engine down reduces the effect but reduces speed and starts to drag the tubes towards the bow. I've had to move the engine directional trim quite a bit to stop her pulling to the right which is now much better at higher speeds (at low speed she still wants to pull right). Extra weight and 'towing' seems to help stability. I'm concerned that the feeling of instability could lead to her hooking up. Other than always towing a ringo with the 18 stone mother in law behind - any ideas welcomed!!!! Coops
__________________
|
|
|
14 November 2016, 16:17
|
#2
|
Member
Country: UK - England
Town: Porchfield
Boat name: Katie
Make: Stingher
Length: 10m +
Engine: Verado 350 x 2
Join Date: Jan 2011
Posts: 697
|
Its called 'Chine - walk ' have a google / search and read all about it
__________________
Fully fledged member of the ‘Bordering negligent and very irresponsible club’.
|
|
|
14 November 2016, 16:44
|
#3
|
Member
Country: UK - England
Town: Newquay
Boat name: Shelly
Make: nawhal
Length: 5m +
Engine: 75
Join Date: Nov 2016
Posts: 13
|
Hi Lee, thanks for the lead and I can see its a big subject! Will immerse myself 'metaphorically speaking' only hopefully....Cheers
__________________
|
|
|
14 November 2016, 18:50
|
#4
|
Member
Country: USA
Town: S. Carolina
Boat name: D560
Make: Avon
Length: 5m +
Engine: 2016 Merc 115hp CT
Join Date: Aug 2013
Posts: 1,277
|
What bolt hole is your engine bolted through?
It may benefit you to raise the engine by one hole position...that way, you can reduce the drag of the lower unit without causing excessive bow lift.
__________________
Richard
Gluing geek since 2007
Opinions and intepretations expressed are solely my own and do not express the views or opinions of my employer
|
|
|
14 November 2016, 18:56
|
#5
|
Member
Country: UK - England
Town: teesside
Boat name: magic
Make: humber 5.5
Length: 5m +
Engine: mariner 115
MMSI: 232012453
Join Date: Apr 2014
Posts: 1,557
|
surely it should do more than 20 knots before it starts getting lairy . I would have expected a 4,8 rib with a 75hp should be cruising comfortably at 20 knots
__________________
|
|
|
14 November 2016, 19:28
|
#6
|
Member
Country: UK - England
Town: Newquay
Boat name: Shelly
Make: nawhal
Length: 5m +
Engine: 75
Join Date: Nov 2016
Posts: 13
|
Hi there, it starts to counterbalance (Chinewalk) at slow planing speeds when the water is very flat - I'' guessing at just over half top speed and we gps's her at 38 knotts. Its really gentle and controllable at low speed and can be dialled put with engine trimmed in. The tubes are definately under inflated based on what I've read also - could this contribute???cheers
__________________
|
|
|
14 November 2016, 19:33
|
#7
|
Member
Country: UK - England
Town: Newquay
Boat name: Shelly
Make: nawhal
Length: 5m +
Engine: 75
Join Date: Nov 2016
Posts: 13
|
Hi - I will check at the weekend - from memory the motor is bolted flush to the transom top - is that what you are asking or are there mounts on the outboard mount (sorry - I'm a newbie!!) Thanks
__________________
|
|
|
14 November 2016, 19:38
|
#8
|
Member
Country: UK - England
Town: Newquay
Boat name: Shelly
Make: nawhal
Length: 5m +
Engine: 75
Join Date: Nov 2016
Posts: 13
|
Image of the vessel.....
__________________
|
|
|
14 November 2016, 19:52
|
#9
|
Member
Country: UK - England
Town: Newquay
Boat name: Shelly
Make: nawhal
Length: 5m +
Engine: 75
Join Date: Nov 2016
Posts: 13
|
Hopefully now attached
__________________
|
|
|
14 November 2016, 20:00
|
#10
|
Member
Country: UK - England
Town: Bristol
Make: Ribcraft
Length: 5m +
Engine: Yamaha
Join Date: May 2006
Posts: 4,299
|
check your engine mount. grad hold of the outboard and see if you can turn it and by how much without the steering turning, just the play in the mounts,, the rib should NOT chinewalk at 20 ffs
__________________
Member of S.A.B.S. West Country Division
|
|
|
14 November 2016, 20:02
|
#11
|
Member
Country: UK - England
Town: South Yorks
Boat name: Black Pig
Make: Ribcraft
Length: 5m +
Engine: DF140a
MMSI: 235111389
Join Date: Feb 2008
Posts: 12,163
|
Could be steering play or worn engine mounts.
__________________
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: Don't feed the troll
|
|
|
14 November 2016, 20:08
|
#12
|
Member
Country: UK - England
Town: South Yorks
Boat name: Black Pig
Make: Ribcraft
Length: 5m +
Engine: DF140a
MMSI: 235111389
Join Date: Feb 2008
Posts: 12,163
|
Quote:
Originally Posted by matt h
check your engine mount. grad hold of the outboard and see if you can turn it and by how much without the steering turning, just the play in the mounts,, the rib should NOT chinewalk at 20 ffs
|
Snap[emoji6]
__________________
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: Don't feed the troll
|
|
|
14 November 2016, 20:15
|
#13
|
Member
Country: UK - England
Town: Newquay
Boat name: Shelly
Make: nawhal
Length: 5m +
Engine: 75
Join Date: Nov 2016
Posts: 13
|
Hi Matt, thanks for the advice, will check. could low pressure in the tubes be an issue?? Thx
__________________
|
|
|
14 November 2016, 20:31
|
#14
|
Member
Country: UK - England
Town: Bristol
Make: Ribcraft
Length: 5m +
Engine: Yamaha
Join Date: May 2006
Posts: 4,299
|
slightly. the tubes will go down a bit in the cold so ideally should be 2-3 psi or firm to touch.
__________________
Member of S.A.B.S. West Country Division
|
|
|
14 November 2016, 20:49
|
#15
|
Member
Country: UK - England
Town: Newquay
Boat name: Shelly
Make: nawhal
Length: 5m +
Engine: 75
Join Date: Nov 2016
Posts: 13
|
Thanks guys for the help - got a good list to check through now, transom height, play in mounts and tube pressure. Once I get back out will post my findings. Great community - cheers
__________________
|
|
|
14 November 2016, 23:18
|
#16
|
Member
Country: UK - Scotland
Town: Denny
Boat name: Highland Bluewater
Length: 6m +
Join Date: Mar 2013
Posts: 1,647
|
Damaged prop ?
__________________
|
|
|
15 November 2016, 09:05
|
#17
|
Member
Country: UK - England
Town: Newquay
Boat name: Shelly
Make: nawhal
Length: 5m +
Engine: 75
Join Date: Nov 2016
Posts: 13
|
Hi Last Tango, that's a good question - the prop on appearance is a little chewed but I'm not getting any significant vibes through the rev range. Keen to understand how the prop could create this kind of instability? Thanks for your help.
__________________
|
|
|
15 November 2016, 11:31
|
#18
|
RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 13,069
|
Can't see on the pic, but you don't have hydrofoils fitted to the engine do you?
__________________
Need spares,consoles,consumables,hire,training or even a new boat?
Please click HERE and HERE and support our Trade Members.
Join up as a Trade member or Supporter HERE
|
|
|
15 November 2016, 11:37
|
#19
|
Member
Country: UK - England
Town: Newquay
Boat name: Shelly
Make: nawhal
Length: 5m +
Engine: 75
Join Date: Nov 2016
Posts: 13
|
Hi there, no we haven't got hydrofoils on the motor......Thanks
__________________
|
|
|
15 November 2016, 12:17
|
#20
|
Member
Country: UK - England
Town: Retford
Boat name: Spy-sea-one
Make: Excel 435
Length: 4m +
Engine: Suzuki Outboard/25/4
Join Date: Oct 2011
Posts: 7,528
|
has the boat got a medium v hull with a planing pad at the stern [flat at the stern not a v all the way through] if its gota a planing pad and the boats badly set up all as mentioned above it will be very unstable. your prop needs sorting if its chewed blades they could be bent all adding to your problems and will cause more.tubes need pumping up to pressure too
__________________
|
|
|
|
|
Thread Tools |
Search this Thread |
|
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
|
Recent Discussions |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|