Reply
 
Thread Tools Search this Thread
 
Old 13 July 2004, 15:19   #1
Member
 
Country: UK - England
Town: Ipswich
Boat name: Obsession
Make: ORKNEY PILOTHOUSE 20
Length: 6m +
Engine: SUZUKI 70
MMSI: 235024496
Join Date: May 2004
Posts: 390
Outboard Height

How high can you fit an outboard on the transom???
What effect will it have on performance???
Will it handle any different at top-end speed
Will it effect speed???
Will it make plan any different???

Sorry for all the questions.

Having problems with it feeling unstable at speed, outboard is offset 35mm
Also when I trim in the Rib dives to port badly,is this due to the engine being to low.

Please help, any suggestion greatfuly recieved.

Thanks
__________________

__________________
Wayne Rogers is offline   Reply With Quote
Old 13 July 2004, 15:34   #2
Member
 
Country: UK - England
Town: Looe
Make: Delta
Length: 4m +
Engine: Mercury
Join Date: Apr 2004
Posts: 1,335
To start with the engine;s cavitation plate ( the one just above the prop) should be in line or just above the bottom of the hull.
If you using a Stainless prop you can usually go one hole up.
You will know if its to high because it will cavitate in a straight line if your running light and cavitate lots when your turning.
If the engine is to low it usually tends to make the boat bow steer, you might find the boat will lean the wrong way when turning.
What sort of revs are you getting out of the engine? You should be able to get 5500rpm max from a 90hp, when trimmed out, do you have to trim it along way out to get it to rev up?
If the engine is to low it will effet your speed as there is more drag in the water and you probably wont be able to rev to the max rpm without trimming out so far that the boat becomes unstable.
Hope this helps
__________________

__________________
Turbodiesel is offline   Reply With Quote
Old 13 July 2004, 15:36   #3
Member
 
Country: UK - England
Town: Looe
Make: Delta
Length: 4m +
Engine: Mercury
Join Date: Apr 2004
Posts: 1,335
Sorry, just read that your 90 is a four stroke!!, you should be able to get the revs to a maximum of 6000rpm (5800 rpm is probably better though so its not running at max revs all the time)
__________________
Turbodiesel is offline   Reply With Quote
Old 13 July 2004, 15:57   #4
Member
 
Country: UK - Wales
Town: St Davids
Boat name: 6 vessels -various
Make: Quinquari/Humber
Length: 10m +
Engine: Twin ETEC200s
Join Date: Nov 2003
Posts: 130
Cavitation plate

[QUOTE=Turbodiesel] To start with the engine;s cavitation plate ( the one just above the prop) should be in line or just above the bottom of the hull.

Sorry Turbo but do disagree. For general seakeeping the cavitation plate should be at a min in line with the hull or up to an inch below. Raising it will achieve optimum revs on an over-proped or under revd engine but the ideal is to have more than req power to achieve revs thus you can drop engine to reduce caviation.

Raising engine is false economy for fuel, engine life and stability long term.

If you are racing and in flat calm waters then I agree with Turbo but otherwise not keen.

Cheers

John
www.quinquari.co.uk
__________________
quinquarimarine is offline   Reply With Quote
Old 13 July 2004, 16:11   #5
Member
 
Country: UK - England
Town: Ipswich
Boat name: Obsession
Make: ORKNEY PILOTHOUSE 20
Length: 6m +
Engine: SUZUKI 70
MMSI: 235024496
Join Date: May 2004
Posts: 390
Thanks for the suggestions,what do you think it is that makes her lean to port if I trim in,it's very severe when it does it,does it at low speed on the plane and at high speed 40-45 MPH
I'm running a alloy prop at present engine revs are spot on.
__________________
Wayne Rogers is offline   Reply With Quote
Old 13 July 2004, 16:48   #6
Member
 
Country: UK - England
Town: Hamble
Length: 9m +
Join Date: Dec 2002
Posts: 2,317
[QUOTE=quinquarimarine]
Quote:
Originally Posted by Turbodiesel
To start with the engine;s cavitation plate ( the one just above the prop) should be in line or just above the bottom of the hull.

Sorry Turbo but do disagree.
Sorry quinquarimarine but do disagree, your suggestion is ok for the 12 seater minibus style rib that you favour, but for general use you wouldn't go wrong following turbodiesels advice.
__________________
It is better to remain silent and be thought a fool, than to speak and remove all doubt!
Dirk Diggler is offline   Reply With Quote
Old 13 July 2004, 18:26   #7
tue
Member
 
Country: UK - England
Town: Paignton, Devon
Make: Chinook and Viking
Length: 7m +
Engine: 150 Etec + 125 Merc
Join Date: Jul 2003
Posts: 526
When I re-fit my engine it is going to be 2 holes up. Apparently this increases top speed. improves handling + something else I can't remember. I'll try and find a thread I started a couple of weeks ago.
__________________
**Paul**
Brixham BSAC
tue is offline   Reply With Quote
Old 13 July 2004, 18:38   #8
tue
Member
 
Country: UK - England
Town: Paignton, Devon
Make: Chinook and Viking
Length: 7m +
Engine: 150 Etec + 125 Merc
Join Date: Jul 2003
Posts: 526
found it Raising engine on transom
__________________
**Paul**
Brixham BSAC
tue is offline   Reply With Quote
Old 14 July 2004, 01:29   #9
Member
 
Pete7's Avatar
 
Country: UK - England
Town: Gosport
Boat name: April Lass
Make: Moody 31
Length: 9m +
Join Date: Aug 2001
Posts: 4,850
Tue, what it might do for you is allow a higher transom so the water doesn't slop in when you have divers getting kitted up always a problem on mine.

Pete
__________________
Pete7 is offline   Reply With Quote
Old 14 July 2004, 04:23   #10
Member
 
Country: UK - England
Town: Looe
Make: Delta
Length: 4m +
Engine: Mercury
Join Date: Apr 2004
Posts: 1,335
The reason you can go up one hole when running a stainless prop is because,
Stainless props can run in less water, they have thinner blades so they create less turbulance in the water and have better grip. they dont bend anywere near as much as ally props. They also grip the water much better because they are much more cupped than ally props which give better performance.
If we ever change a ally prop to a stainless the engine should be lifted by one hole and the pitch should go up by one.
This is of course all in theory!! usually its very much trial and error. If we are rigging a boat at Barrus we will take it out and prop test it to make sure its all set up ok. Thats ok for us because we have all the props we need, i think for most people they dont have the endless amounts of props they can try!!
__________________

__________________
Turbodiesel 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 17:32.


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