Reply
 
Thread Tools Search this Thread
 
Old 14 October 2013, 12:13   #111
Member
 
Country: USA
Town: Portland, OR
Make: Zodiac F470
Length: 4m +
Engine: Suzuki DF25EL
Join Date: Jun 2013
Posts: 229
Speaking of evil anti-cavitation plate. or anti-ventilation plate. Why then every outboard manufacturer calls them anti-cavitation plate? (see #5) Wouldn't they know better? One thing for sure if motor is trimmed -in it will act as one big mighty trim tab lifting stern up and pushing blow down.
__________________

__________________
SIBRider is offline   Reply With Quote
Old 14 October 2013, 12:47   #112
Member
 
The Gurnard's Avatar
 
Country: UK - Scotland
Town: Stirling
Boat name: The Gurnard
Make: Quicksilver
Length: 4m +
Engine: mariner 25hp 2s
Join Date: Jul 2013
Posts: 986
Quote:
Originally Posted by Projectile View Post
Would appreciate it if anybody might be able to take some similar pics of the junction of their hull with transom ...


Not sure if this will help you but here is a photo of the rear of my 4.3 Quicksilver SIB.
As far as I am concerned, mine is well trimmed and has no bad handling characteristics, either lightly loaded ..with only me, the fuel tank an engine at the rear of the boat.. or laden with more weight up front. No water spray either over the back from the 25hp Mariner 2 stroke even at full throttle.
The nose is higher in the air when lightly loaded with weight at the back..but as soon as it starts planning ..she is level. Heavy loaded with weight up front..the nose doesn’t go quite so high before planning..but once she does...the boat zips along level.
From the photo below .. there is quite a hook on mine too .. so Im not so sure that is your problem ?
I drew the white line to help highlight the hook..the greyish lines are the keel strip on the bottom of the boat



__________________

__________________
The Gurnard is offline   Reply With Quote
Old 14 October 2013, 15:49   #113
Member
 
Projectile's Avatar
 
Country: Canada
Boat name: WB465
Make: Zodiac
Length: 4m +
Engine: 2013 ETEC 30
Join Date: Dec 2012
Posts: 254
SIBRider:

Thanks again for all of your input. I really appreciate everybody here trying to help me out.

The photo below shows that a hook includes an upturn in the hull, like an upside down cup, just as you describe. This will act like a trim tab, too.

You have a futura hull on your boat, so when you plane, your boat rides considerably if not mostly on the speed tubes, much higher up and out of the water than my boat which has a conventional SIB hull. I could imagine that that might mitigate the effect of a hook in the center of your hull.

Nobody disagrees that a motor that is trimmed in will bring the bow down. I just can't keep describing over and over how trimming the motor out does not solve the problem that I have with the bow coming down as I accelerate beyond planing speed.

When my A/C plate was 3 inches below the bottom of the transom, I trimmed the motor all the way out. The bow down attitude got slightly better, but was still a huge problem. In the 4th or 5th trim holes up and away from the transom, the A/C plate started to become visible at the water line and cavitation emerged. That's not a big suprise since the prop was brought close to the surface of the water. Now that my A/C plate is about 1/2 inch below the transom, the bow down attitude is better, but still problematic. Furthermore, now I have cavitation all the time that got worse as I trimmed out (to address the bow down attitude) and got better with an additional 200-240 lbs in the boat. Since the bow down attitude is present as I accelerate from planing speed whether the motor is low or at proper height, and whether the engine is trimmed in or out, it is IMPOSSIBLE for trim to be THE cause of my bow-down problem.

Either the boat was designed and is supposed to run with the bow down as I experience, or there is a problem with the hull. I find the former hard to believe.
Attached Thumbnails
Click image for larger version

Name:	hollows2.jpg
Views:	67
Size:	38.6 KB
ID:	86386  
__________________
Projectile is offline   Reply With Quote
Old 14 October 2013, 15:50   #114
Member
 
Projectile's Avatar
 
Country: Canada
Boat name: WB465
Make: Zodiac
Length: 4m +
Engine: 2013 ETEC 30
Join Date: Dec 2012
Posts: 254
The Gunard:

Thanks for posting the pic. I think that I have a much more prominent hook in my hull than that.
__________________
Projectile is offline   Reply With Quote
Old 14 October 2013, 16:17   #115
Member
 
Country: USA
Town: Portland, OR
Make: Zodiac F470
Length: 4m +
Engine: Suzuki DF25EL
Join Date: Jun 2013
Posts: 229
Well. If think it's such a concern. You can glue/screw piece of 1/2 or whatever is appropriate size plastic (HDPE for example) to bottom of rear panel to push keel down. Shouldn't be that big of deal.

That's one huge cup/hook on that boat.
__________________
SIBRider is offline   Reply With Quote
Old 14 October 2013, 21:08   #116
Member
 
Projectile's Avatar
 
Country: Canada
Boat name: WB465
Make: Zodiac
Length: 4m +
Engine: 2013 ETEC 30
Join Date: Dec 2012
Posts: 254
That's not what my WB465 looks like at WOT (but I wish it did). Spray is coming up just fore of the aft carrying handle, while it comes up fore of the fore carrying handle on mine.

That's just not normal.
Attached Thumbnails
Click image for larger version

Name:	WB465 planing.jpg
Views:	78
Size:	34.1 KB
ID:	86397  
__________________
Projectile is offline   Reply With Quote
Old 14 October 2013, 22:28   #117
Member
 
Country: USA
Town: Pooler, Georgia
Boat name: not applicable
Make: Avon
Length: 3m +
Engine: Outboard
Join Date: Aug 2011
Posts: 156
Seems we are comparing a boat supported by speed tubes plus the hull extension sponsons to a straight inflatable with no speed tubes. They are two different designs and susceptible to different hydraulic conditions in use.

What The Gurnard posted is pretty close to ideal for the design.

The picture Projectile posted is what he should see with his boat, not a bow steered hull which could be dangerous at sea.
__________________
frankc is offline   Reply With Quote
Old 14 October 2013, 23:38   #118
Member
 
Projectile's Avatar
 
Country: Canada
Boat name: WB465
Make: Zodiac
Length: 4m +
Engine: 2013 ETEC 30
Join Date: Dec 2012
Posts: 254
Not exactly the same angle, but still a reasonable side by side comparison:
Attached Thumbnails
Click image for larger version

Name:	WB465 planing.jpg
Views:	72
Size:	34.1 KB
ID:	86398   Click image for larger version

Name:	Screen Shot 2013-10-14 at 9.30.56 PM.png
Views:	91
Size:	246.6 KB
ID:	86399  
__________________
Projectile is offline   Reply With Quote
Old 15 October 2013, 03:31   #119
Member
 
Country: USA
Town: Portland, OR
Make: Zodiac F470
Length: 4m +
Engine: Suzuki DF25EL
Join Date: Jun 2013
Posts: 229
Quote:
Originally Posted by Projectile View Post
Not exactly the same angle, but still a reasonable side by side comparison:
then again even judging by tiller handle angel. Yours point up theirs just about level. Your motor is significantly more trimmed-in then theirs.
__________________
SIBRider is offline   Reply With Quote
Old 15 October 2013, 07:02   #120
Member
 
Country: USA
Town: Pooler, Georgia
Boat name: not applicable
Make: Avon
Length: 3m +
Engine: Outboard
Join Date: Aug 2011
Posts: 156
The gentleman reported that even when trimmed out to the point that cavitation became extreme, it still bow steered. He then posted pictures showing a cup in the bottom of the hull. I certainly take his word for that.

Why do you feel that his only problem is cavitation and the bow steer does not exist? What radial thrust component results from cavitation which would depress the bow of the boat? Have you ever run a boat with a hook in the bottom?
__________________

__________________
frankc 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 08:24.


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