Reply
 
Thread Tools Search this Thread
 
Old 13 March 2018, 20:18   #1
Member
 
Lee1's Avatar
 
Country: UK - England
Town: South East
Make: Waveline V SIB
Length: under 3m
Engine: Mercury 25hp
Join Date: Sep 2017
Posts: 384
Mercury Thunderbolt 7.5hp 2 or 3 blade prop?

I have acquired 2 vintage Mercury 7.5hp thunderbolts.

A long shaft with a three blade prop (slightly earlier model than the short shaft and only good for parts)

A standard shaft with a 2 blade prop. All there with 165psi compression but not running yet!!

I've seen on YouTube vids that all the standard shaft 7.5 and 9.8 thunderbolts have the 2 blade prop not the 3 so I'm guessing the 3 blade was fitted only to the long shaft for thrust use on large displacement sail boats? Or I'm wrong and the long shaft I have has had a different prop fitted (it is painted red not black) and the long shaft had a 2 blade prop originally fitted as well? If the 3 blade prop on the long shaft is the original prop Mercury must have done some testing and decided to use a 3 blade not a 2 if so I wonder why as no other outboards of these sizes use a 2 blade prop?

I've advertised the outboard for sale but I'm considering keeping them and if the standard shaft is an easy fix (when I look at it in depth tomorrow) I will keep it and use it as my back up for this season and something to enjoy using and testing out both props on a 2.7 v honwave sib.

Also if the standard shaft is a keeper what prop will give me the best top end speed? I'm guessing the 3 blade.

Also any suggestions for a better prop for use on this Mercury Thunderbolt 7.5hp standard shaft for SIB use other than the 2 props I already have, many thanks

Click image for larger version

Name:	IMG_5943.jpg
Views:	61
Size:	130.8 KB
ID:	123794
Click image for larger version

Name:	IMG_5939.jpg
Views:	59
Size:	126.4 KB
ID:	123795
Click image for larger version

Name:	IMG_5936.jpg
Views:	78
Size:	167.7 KB
ID:	123796
Click image for larger version

Name:	IMG_5932.jpg
Views:	59
Size:	134.9 KB
ID:	123797
__________________

__________________
Lee1 is offline   Reply With Quote
Old 14 March 2018, 04:37   #2
Member
 
Country: UK - England
Town: Southampton
Boat name: SMH Rib / War Shot
Make: Ribtec / Scorpion
Length: 4m +
Engine: 10hp Yam / 150hp opt
Join Date: Sep 2003
Posts: 1,921
RIBase
I've seen both 2 and 3 blade propellers on those old Mercs.
The number of blades will have less effect than the pitch and the condition of the propellers.
You'll need to try both and see which one performs best.

That being said, the two blade will be more efficient as it has less blade area to drag through the water.
__________________

__________________
Searider is offline   Reply With Quote
Old 14 March 2018, 11:34   #3
Member
 
Lee1's Avatar
 
Country: UK - England
Town: South East
Make: Waveline V SIB
Length: under 3m
Engine: Mercury 25hp
Join Date: Sep 2017
Posts: 384
Unfortunately this one won't be running, see my post on the engine thanks for your reply
__________________
Lee1 is offline   Reply With Quote
Old 31 May 2018, 17:13   #4
Member
 
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,618
My 60 is a similar vintage and pushes my humber along nicely.

If it works for your setup chill and enjoy the boating.
__________________
9D280 is offline   Reply With Quote
Old 01 June 2018, 10:25   #5
Member
 
Lee1's Avatar
 
Country: UK - England
Town: South East
Make: Waveline V SIB
Length: under 3m
Engine: Mercury 25hp
Join Date: Sep 2017
Posts: 384
Very true!
__________________
Lee1 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 05:21.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.