Reply
 
Thread Tools Search this Thread
 
Old 11 July 2014, 12:47   #31
Member
 
Country: USA
Town: Portland, OR
Make: Zodiac F470
Length: 4m +
Engine: Suzuki DF25EL
Join Date: Jun 2013
Posts: 229
Running on first hole should not be norm unless you have near vertical transom. Not much point trying to figure out what's wrong here.

Can you measure transom angle relative to floor boards?

Motor in second and/or third trim hole place level or ruler on AV plate. Where does it project relative to transom?
__________________

__________________
SIBRider is offline   Reply With Quote
Old 11 July 2014, 13:10   #32
Member
 
Projectile's Avatar
 
Country: Canada
Boat name: WB465
Make: Zodiac
Length: 4m +
Engine: 2013 ETEC 30
Join Date: Dec 2012
Posts: 254
In second or third hole, A/V plate is 3/4-1 inch below bottom of transom.

The most likely problem is that motor is too high. This would explain why ventilation gets better with more weight and worse as I trim out (up). Lowering engine will permit me to trim out to 2nd or 3rd hole.

RPM readings are not consistent with need for a higher pitch prop. Lower pitch, if anything, is more likely.

I plan to drop motor 1 inch and re-test.
__________________

__________________
Projectile is offline   Reply With Quote
Old 11 July 2014, 14:06   #33
Member
 
Country: USA
Town: Portland, OR
Make: Zodiac F470
Length: 4m +
Engine: Suzuki DF25EL
Join Date: Jun 2013
Posts: 229
Re-reading last year topic. Seems you raised motor about 2" with metal plate. Prior to that you had tested motor with 3/4 plank and that did not produce desired result. You said no improvement. Seems dropping 1" from current position you'd be back to square one or very close to that.

Makes me think you should focus on propulsion still. Can you confirm what you current prop is?

When you say you reached only 5300 RPMs on 2 hole WOT ventilating?
Was it babying, watching for ventilation or true WOT twist it all the way? It seems usually, ventilating prop experiences loss of resistance. Naturally leading to RPMs going up without restriction. Certainly my motor behaves this way. Going as far as hitting hitting rev-limiter.
__________________
SIBRider is offline   Reply With Quote
Old 11 July 2014, 16:18   #34
Member
 
Projectile's Avatar
 
Country: Canada
Boat name: WB465
Make: Zodiac
Length: 4m +
Engine: 2013 ETEC 30
Join Date: Dec 2012
Posts: 254
First, let me say a big thank-you for going back and re-reading the old thread and really trying so hard to help me out, SIBRider.

It turns out that back at that time, when I was having huge problems with bow down on acceleration and huge stress on the boat (but no ventilation unless trimmed out to hole 4 or 5), my boat was not correctly assembled. YOU actually brought this to my attention when you noticed a difference in the positioning of the floorboards relative to the elephant trunk hole on my transom. My dealer had not placed the rear floorboard over the groove on the transom, but rather, had it sitting on top of that groove. Accordingly, the floorboards would have been too short. The problems I was having then are perfectly described by a hook in the hull, and incorrect floorboard assembly would be expected to cause just that. Unfortunately, it went noticed, and all the attention and advice I received from the dealer that sold me the boat (Defender) and the dealer that assembled it and look after me locally (Automarine) was focused on the motor being too low.

When the transom was plated to raise the motor 2 inches, the boat was also reassembled properly.

Things got much better. The bow down attitude improved considerably. However, I had a new problem: ventilation as you see in the video in this thread. I have to operate the boat in the first trim hole, which, I think, also keeps the bow somewhat down (but that problem isn't near;y as bad as before).

I now believe that the original problems I had were due to incorrect floorboard assembly, and that the problems I am having now are due to the motor being too high. I suspect that plating my transom to raise it was never required. A 3/4 inch plank and proper assembly would probably have done the trick.

So at the end of the day, I suspect that the ideal position for my AV plate will be about 2 inches below transom bottom. I should be able to run in the second trim hole at that level, and then I will recheck the WOT RPM and see if I need a lower pitch prop.

My current prop is the Evinrude OEM prop I described earlier and that you mentioned here.

The engine reached 5200 RPM (and change) in trim hole 1 with intermittent ventilation raising RPM to 5600 when it was happening.

The engine reached 5300 RPM (and change) in trim hole 2 with more frequent ventilation also raising RPM to around 5600 when it was happening.
__________________
Projectile is offline   Reply With Quote
Old 11 July 2014, 17:25   #35
Member
 
Country: USA
Town: Portland, OR
Make: Zodiac F470
Length: 4m +
Engine: Suzuki DF25EL
Join Date: Jun 2013
Posts: 229
Lots of variables. Certainly worthy experiment.
at 5600 RPM do you let go throttle or it goes down by itself? 4 blade prop is something that can certainly address this problem or higher rake 3 blade.

Mine 3 blade has notable rake.
__________________
SIBRider is offline   Reply With Quote
Old 11 July 2014, 18:12   #36
Member
 
Projectile's Avatar
 
Country: Canada
Boat name: WB465
Make: Zodiac
Length: 4m +
Engine: 2013 ETEC 30
Join Date: Dec 2012
Posts: 254
RPM goes down by itself.
__________________
Projectile is offline   Reply With Quote
Old 01 August 2014, 13:42   #37
Member
 
Projectile's Avatar
 
Country: Canada
Boat name: WB465
Make: Zodiac
Length: 4m +
Engine: 2013 ETEC 30
Join Date: Dec 2012
Posts: 254
I've been boating in the Okanagan, which is not at as high an altitude as Calgary. Here, I get 24 mph with my ETEC 30 at 5380 RPM in the second trim hole (1 mph extra and about 100 rpm higher than Calgary).

I still get intermittent ventilation but it's not that common anymore. It seems to be very sensitive to keel pressure. Interestingly, I get it if the keel is inflated to manufacturer's recommended pressure of 3.5 psi, but not if I pump it up to 5-6 psi.

It's also very sensitive to port-starboard weight distribution - something I never experienced in any of my other Zodiacs.

All in all, this 2 weeks vacation has been a blast and the boat has been performing mostly pretty well. I am inclined to try to get rid of the remaining intermittent ventilation with a new propeller rather than lowering the motor at this point
__________________
Projectile is offline   Reply With Quote
Old 01 August 2014, 13:47   #38
Member
 
Projectile's Avatar
 
Country: Canada
Boat name: WB465
Make: Zodiac
Length: 4m +
Engine: 2013 ETEC 30
Join Date: Dec 2012
Posts: 254
3 questions:

1) What propeller to get? (Current prop is Evinrude OEM 3 blade 10.3 x 12)

2) A lower pitch prop will increase my RPM, which seems to be needed to get me into the sweetspot for this motor (5500-6000), but what will this do to my fuel economy and performance?

3) If I go to a 4 blade prop, what pitch should I aim for when going from 3 blade to 4 blade?
__________________
Projectile is offline   Reply With Quote
Old 01 August 2014, 13:58   #39
Member
 
Country: USA
Town: Seattle
Boat name: Water Dog
Make: Polaris
Length: 4m +
Engine: Yamaha 60hp
Join Date: Apr 2007
Posts: 1,152
Quote:
Originally Posted by Projectile View Post

I still get intermittent ventilation but it's not that common anymore. It seems to be very sensitive to keel pressure. Interestingly, I get it if the keel is inflated to manufacturer's recommended pressure of 3.5 psi, but not if I pump it up to 5-6 psi.
This is my experience as well. The lower pressure allows the keel to compress and the fabric of the hull to bow and that creates a hook.

Frustrating that the floorboard issue created the motor height issue and now the ventilation issue. Goes to show you how one design/assembly element can really mess with a lot of different performance problems.
__________________
captnjack is offline   Reply With Quote
Old 01 August 2014, 22:34   #40
Member
 
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,653
Quote:
Originally Posted by Projectile View Post
3) If I go to a 4 blade prop, what pitch should I aim for when going from 3 blade to 4 blade?
Assuming all other variables (cupping, blade shape, all that) are the same, I've generally heard that you lose about the equivalent of 1" of pitch in rpm going 3 blade to 4 (more rotational drag, more weight.)

Unfortunately, all the other variables are never the same, so...

jky

Okay, that was clear as mud. #blade to 4, you'll need to drop an inch or so in pitch to get the same rpm. Take that with a grain of salt. The rules of thumb all depend on whose thumb you're measuring with.
__________________

__________________
jyasaki 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 14:13.


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