Reply
 
Thread Tools Search this Thread
 
Old 08 September 2015, 13:07   #1
Member
 
Country: UK - England
Town: Horley
Make: Yamaha 3.1 STI
Length: 3m +
Engine: 9.8 Tohatsu 2 stroke
Join Date: Sep 2013
Posts: 246
Nose of sib to high

I have been looking in the search items, but not very good searcher so sorry if I missed a previous thread on this
Anyway (boat Yamaha 3.1 sti motor Tohatsu 9.8)
Running in now a 3/4 throttle the nose is up way to high, will this level out at wot or get worse?, the motor is on the first notch and I sit in the middle on a bean bag, the air floor is at the correct pressure
I see zodiac sell some fins to put on the back, but they look like they will get in the way of the transom wheels, or a hydrofoil fitted the the outboard help, or I see some people talk about packing the outboards up
I'm haven't got an anchor yet so would the weight of that help?
Just trying to preempt if I have a problem as I'm off to the boat show next week
__________________

__________________
Mickhitchuk is offline   Reply With Quote
Old 08 September 2015, 13:12   #2
Member
 
Country: UK - England
Town: East Anglia
Boat name: Nimrod II
Make: Aerotec 380
Length: 3m +
Engine: Suzuki DF20 EFI
Join Date: Nov 2007
Posts: 3,279
I wonder if you are running at transition speed from displacement to plane? This speed usually has a very bow up attitude until a full plane is achieved and is an attitude you wold normally pass through as quickly as possible.
__________________

__________________
Fenlander is offline   Reply With Quote
Old 08 September 2015, 13:18   #3
Member
 
Nick Hearne's Avatar
 
Country: UK - England
Town: Bucks
Boat name: Blue & Ding Dong
Make: Ribeye,SR4 & Bombard
Length: 6m +
Engine: 115,50 & 15Hp Yams
Join Date: Feb 2004
Posts: 3,242
When you say the engine is on the first notch do you mean the one nearest the transom? As the leg is as close to the transom as it can be?
If not move it in closer to the transom,
__________________
Member of the Ribeye supporters club!!!
Member of Bombard 380 Aerotec club
Member of SR4 club
Nick Hearne is offline   Reply With Quote
Old 08 September 2015, 13:57   #4
Member
 
Country: UK - England
Town: Horley
Make: Yamaha 3.1 STI
Length: 3m +
Engine: 9.8 Tohatsu 2 stroke
Join Date: Sep 2013
Posts: 246
Thxs Nick, yes the leg of the motor is as close to the transom as it could be, fenlander could be right as I only had it a wot for 1 minute
__________________
Mickhitchuk is offline   Reply With Quote
Old 08 September 2015, 13:59   #5
Member
 
Country: UK - England
Town: Bristol
Make: Ribcraft
Length: 5m +
Engine: Yamaha
Join Date: May 2006
Posts: 4,194
Fenlander is totally right. Its a short sib! Nothing to worry about and first notch is correct
__________________
Member of S.A.B.S. West Country Division
matt h is offline   Reply With Quote
Old 08 September 2015, 14:00   #6
Member
 
beerbelly's Avatar
 
Country: UK - England
Town: teesside
Make: valiant v570
Length: 5m +
Engine: mercury 100
MMSI: 232012453
Join Date: Apr 2014
Posts: 859
just crack it wide open and you should climb over the water and onto the plane then just back off to a comfortable cruising speed
__________________
beerbelly is offline   Reply With Quote
Old 08 September 2015, 14:02   #7
Member
 
Country: UK - England
Town: Horley
Make: Yamaha 3.1 STI
Length: 3m +
Engine: 9.8 Tohatsu 2 stroke
Join Date: Sep 2013
Posts: 246
Who looking forward to getting it run in
__________________
Mickhitchuk is offline   Reply With Quote
Old 08 September 2015, 14:03   #8
Member
 
Country: UK - England
Town: Horley
Make: Yamaha 3.1 STI
Length: 3m +
Engine: 9.8 Tohatsu 2 stroke
Join Date: Sep 2013
Posts: 246
Doh I mean whoo hoo
__________________
Mickhitchuk is offline   Reply With Quote
Old 08 September 2015, 14:54   #9
Member
 
lightning's Avatar
 
Country: UK - England
Town: Marple
Make: Zodiac
Length: under 3m
Engine: Tohatsu 9.8
Join Date: Jun 2009
Posts: 585
I have a similar setup. Zodiac 2.85 Solid with Tohatsu 9.8

Two up the boat will achieve about 4mph nose down at 2,000rpm. (I have a tacho fitted) after this the nose does start to rise.
This continues until 3,200rpm when the nose is right up and still only 6mph. (with great big wash)

Then an extra 300rpm sees it plane, and then it's off, rapidly accelerating to 15mph+. The bow comes down and the wash reduces greatly.

2,000 rpm is achieved with the throttle just past the "start" position.

I have tried all five trim positions and it ended up in the middle one. However there was a fair bit of splashback at planing speeds. This was completely solved by raising the engine on the transom 2cm with a block of wood.

As a start point the engine leg should be at 90 degrees to the water at trolling speed.

I also tried a higher pitch prop. This reduced the RPM making the boat plane at 2800rpm rather than 3300rpm. The RPM was down from 5500 to 5000 at WOT. Max speed was the same! 19-20mph.

However it took a bit longer to plane where with the standard prop it's instant. So l fit the standard prop for Scotland and the higher pitch one for the canal/broads etc where it's lower revving at 4-6 mph.
__________________
lightning is offline   Reply With Quote
Old 08 September 2015, 16:05   #10
Member
 
Country: UK - England
Town: Sussex
Boat name: Bombard, Y-162
Make: Aerotec 380, Y-Class
Length: 3m +
Engine: Mercury Mariner 15hp
Join Date: Jul 2010
Posts: 2,692
Unless you have some weight up front most SIB's are pretty nose up and a bit hairy in a blowy head sea. Definitely get some ballast up there with fuel, gear (incl anchor) or whatever.
__________________

__________________
Max... is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 11:51.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.