Reply
 
Thread Tools Search this Thread
 
Old 09 October 2014, 04:50   #1
Member
 
Country: New Zealand
Town: Dunedin
Boat name: Zebedee
Make: Zodiac
Length: 3m +
Engine: Mariner 15 2 stroke
Join Date: Aug 2001
Posts: 73
Reducing prop pitch for heavier loads?

Hi all,

Have been running an air floor Zodiac Classic MkIIC with 15hp Mariner 2 stroke for a few years. It was great when the 3 kids were pretty small - all 5 of us planed comfortably. Now the kids are a lot bigger - all up load with 5 is probably 370kg, compared with 290kg when we started. Now we can't plane with all on board. (But when 3 wait on the beach, knee-boarding behind still works a treat.)

So here's my question: are we likely to be able to get planing again by dropping to a 7 inch pitch prop? (Current prop is Mercury Black Max 3 blade 9 inch diameter, 8 inch pitch). I know I'll lose top end speed, I'm choosing not to care about that. I haven't really got a feel for how much difference an inch will make ...

All suggestions and speculation welcome. (I know, I need a bigger boat/engine - not an option for now.)

cheers,
Simon
__________________

__________________
Simon Guest is offline   Reply With Quote
Old 09 October 2014, 05:20   #2
Member
 
dave3235's Avatar
 
Country: UK - England
Town: Bristol
Boat name: Salty Cheeks
Make: Honwave
Length: 3m +
Engine: 20hp 2stroke Mariner
Join Date: Mar 2014
Posts: 448
[QUOTE=Simon Guest;650094]Hi all,

Have been running an air floor Zodiac Classic MkIIC with 15hp Mariner 2 stroke for a few years. It was great when the 3 kids were pretty small - all 5 of us planed comfortably. Now the kids are a lot bigger - all up load with 5 is probably 370kg, compared with 290kg when we started. Now we can't plane with all on board. (But when 3 wait on the beach, knee-boarding behind still works a treat.)

So here's my question: are we likely to be able to get planing again by dropping to a 7 inch pitch prop? (Current prop is Mercury Black Max 3 blade 9 inch diameter, 8 inch pitch). I know I'll lose top end speed, I'm choosing not to care about that. I haven't really got a feel for how much difference an inch will make ...

All suggestions and speculation welcome. (I know, I need a bigger boat/engine - not an option for now.)

cheers,
You could try it but 1 pitch lower which will raise the revs by 2 to 300 rpm's.You are probably at the max weight wise.You could get a 7p and send it to steel developments and they could take it to a 6p which would be more noticeable in raising the revs hope this helps.
__________________

__________________
dave3235 is offline   Reply With Quote
Old 09 October 2014, 06:02   #3
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: 3,275
Your Classic is probably rated to 35hp so for a full load you are under engined. You are also already down a pitch on the standard 9 prop fitted from new. In the same circumstance (Honwave alloy floor 3.5m with Mariner 15) I just accepted the non-plane when fully loaded to avoid the expense of a second prop and possible over-rev when normally loaded.
__________________
Fenlander is offline   Reply With Quote
Old 09 October 2014, 06:59   #4
Member
 
Country: UK - Scotland
Make: Destroyer 5.5/Ring18
Length: 3m +
Engine: Yam 90HP/Yam200HP
Join Date: Jul 2009
Posts: 447
35HP when fitted with floor boards.
25HP when fitted with an air floor
At least that's what mine said on the spec plate on the transom.
__________________
69cmw is offline   Reply With Quote
Old 09 October 2014, 09:04   #5
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: 2,691
Quote:
Originally Posted by Simon Guest View Post
...Now the kids are a lot bigger - all up load with 5 is probably 370kg........are we likely to be able to get planing again by dropping to a 7 inch pitch prop?
In a nutshell, no chance! That is a hell of a load for a little 15 to cope with - either lose the load or increase the power. No other practical option.
__________________
Max... is offline   Reply With Quote
Old 09 October 2014, 10:22   #6
Member
 
paddlers's Avatar
 
Country: UK - England
Town: Sticks, N.Yorks
Boat name: Tamanco
Make: Honwave 3.5AE
Length: 3m +
Engine: Tohatsu Outboard
Join Date: May 2012
Posts: 1,063
I'm afraid the above advice seems good. My Honwave 3.5 Ally floor planes easily with 5 of us with the 20hp Tohatsu (max on transom plate) four stroke but won't get out with my Mercury 15 2 stroke with stainless prop.

I can't believe the extra 5 horses make so much difference!
__________________
paddlers is offline   Reply With Quote
Old 09 October 2014, 10:55   #7
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: 2,691
Quote:
Originally Posted by paddlers View Post

I can't believe the extra 5 horses make so much difference!


It's a more than 30% increase in power, not just 5 horses. Like going from a 150 hp saloon to the souped up 195hp one.
__________________
Max... is offline   Reply With Quote
Old 09 October 2014, 11:00   #8
Member
 
paddlers's Avatar
 
Country: UK - England
Town: Sticks, N.Yorks
Boat name: Tamanco
Make: Honwave 3.5AE
Length: 3m +
Engine: Tohatsu Outboard
Join Date: May 2012
Posts: 1,063
Quote:
Originally Posted by Max... View Post
It's a more than 30% increase in power, not just 5 horses. Like going from a 150 hp saloon to the souped up 195hp one.
And you know it straight away. I always imagined the 2 stroke element might have narrowed the gap!
__________________
paddlers is offline   Reply With Quote
Old 09 October 2014, 12:55   #9
Member
 
Peter_C's Avatar
 
Country: USA
Boat name: Uh...a kayak?
Length: 4m +
Join Date: Dec 2009
Posts: 1,485
I dropped my prop pitch from 17" down to 15" since the boat is most often loaded heavy. It definitely helped. I also have a Stingray lifting wing on the motor that keeps the bow down and allows the boat to plane at around 12 MPH, with 6 people onboard (No dive gear).
__________________
Peter_C is offline   Reply With Quote
Old 10 October 2014, 22:13   #10
Member
 
Country: New Zealand
Town: Dunedin
Boat name: Zebedee
Make: Zodiac
Length: 3m +
Engine: Mariner 15 2 stroke
Join Date: Aug 2001
Posts: 73
Thanks for all the input. Maybe I should look at slightly larger engines, then. I do recall, though, standing in the London Boat Show about 10 years ago, walking around carrying a 15hp was just fine, but a 25hp I could hardly lift. My Mariner 15hp 2 stroke weighs 35kg. The Mariner 25hp 2 stroke weighs 48kg. Tohatsu 25hp is similar. Tohatsu 18hp only 41kg, but I can hardly justify buying a new engine for another 3hp.

Ah well, Summer's coming (for us Southern Hemisphere folk). Happy days ...

cheers,
Simon
__________________

__________________
Simon Guest 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 22:12.


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