Reply
 
Thread Tools Search this Thread
 
Old 14 June 2015, 15:28   #1
Member
 
Country: UK - England
Town: South Coast
Boat name: Scooby Doo
Make: Arctic Blue 27
Length: 8m +
Engine: QSD 4.2 350 Diesel
Join Date: Jun 2015
Posts: 28
Prop advice for stepped 50kn 8.2m diesel rib

Hi everyone,

I'm new here but have been lurking for a while. I run an Arctic Blue 27 with a double stepped hull, 350hp diesel and bravo 1 x diesel drive. She's 3 tonnes on the water and does 50knts.

I'm currently running a 28P Bravo 1 prop and was wondering if switching to a 3 bladed Mirage Pro would increase the top end a little. I've also been led to believe its normal to up the pitch by 1 when changing from Bravo 1 to Mirage Pro?

With the 28P Bravo 1 she runs well at max RPM at WOT at normal load.

Any advice would be gratefully received.
__________________

__________________
Scooby Doo is offline   Reply With Quote
Old 15 June 2015, 13:10   #2
Member
 
Country: UK - England
Town: South Coast
Boat name: Scooby Doo
Make: Arctic Blue 27
Length: 8m +
Engine: QSD 4.2 350 Diesel
Join Date: Jun 2015
Posts: 28
I need to buy a new prop as a spare and was wondering if its worth taking a punt on a Mirage Pro to free up a few more knots top end.

Worry is it'll get les grip in the corners and cavitate more when pulling off. I've read the US threads which have lots of info for Outboards but nothing for inboard boats.

Has anyone swopped from Mirage Pro to Bravo 1 or visa versa?
__________________

__________________
Scooby Doo is offline   Reply With Quote
Old 15 June 2015, 14:50   #3
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: 1,894
RIBase
Have you looked at the mercury propeller selector on their website?
__________________
Searider is offline   Reply With Quote
Old 16 June 2015, 16:54   #4
Member
 
kubcat's Avatar
 
Country: Australia
Town: Sydney
Boat name: Lunasea
Make: Ribtec 890SX
Length: 8m +
Engine: Yamaha ME 421STI x 2
Join Date: Aug 2009
Posts: 470
Prop advice for stepped 50kn 8.2m diesel rib

50 knots is moving for such a big boat.

There is a guy on the offshore boat forums that has a prop shop that is considered the guru for fast boats your size and above. Stern drives are his specialty.

He is in the U.S but we have racers in Australia sending him props for tweaking.

Google BBlades.
__________________
kubcat is offline   Reply With Quote
Old 16 June 2015, 17:00   #5
Member
 
Country: UK - England
Town: Mighty Penryn
Boat name: Little Joe.
Make: Avon Searider
Length: 4m +
Engine: Honda BF50
Join Date: Aug 2005
Posts: 8,841
That must be a very smart hull if that rig will do 50knts.
__________________
Mollers is offline   Reply With Quote
Old 16 June 2015, 23:08   #6
Member
 
Country: UK - England
Town: South Coast
Boat name: Scooby Doo
Make: Arctic Blue 27
Length: 8m +
Engine: QSD 4.2 350 Diesel
Join Date: Jun 2015
Posts: 28
Thanks for the replies I've sent an email to a couple of prop guru's in the states and got some really helpfull answers. Looks like the

The hull is fairly nippy, double stepped with tricky chimes. The cavitation plate is pretty close to the bottom of the V which helps top end with a good prop. Below is a link to a really bad picture of the hull. I will post some better pics once I get home (early July).

The hull is the 2nd generation; the 1st was based on a Norwegian racing rib hull. The crazy Norwegians have one of these boats with a 700hp V10 that pushes 70-80knots. So I'm not even stretching its legs at 50.

Hello from the Solent
__________________
Scooby Doo is offline   Reply With Quote
Old 17 June 2015, 14:22   #7
Member
 
Country: UK - England
Town: Mighty Penryn
Boat name: Little Joe.
Make: Avon Searider
Length: 4m +
Engine: Honda BF50
Join Date: Aug 2005
Posts: 8,841
Quote:
Originally Posted by Scooby Doo View Post
The crazy Norwegians have one of these boats with a 700hp V10 that pushes 70-80knots. So I'm not even stretching its legs at 50.
As you have half of the horsepower and more weight, that's impressive.
__________________
Mollers is offline   Reply With Quote
Old 17 June 2015, 20:06   #8
Member
 
Country: UK - England
Town: South Coast
Boat name: Scooby Doo
Make: Arctic Blue 27
Length: 8m +
Engine: QSD 4.2 350 Diesel
Join Date: Jun 2015
Posts: 28
The boat weighs 2.7t light and 3t heavy. One of the reasons for the good speed is the engines huge torque, 704nm (519ft-lbs)! Which means it can turn a high pitch prop, pretty much the highest pitch mercury make.
__________________
Scooby Doo is offline   Reply With Quote
Old 18 June 2015, 06:04   #9
B58
Member
 
Country: UK - England
Town: Aylesbury
Length: no boat
Engine: Diesel/Petrol
Join Date: Jun 2014
Posts: 1
I wouldn't recommend Mirage Plus, its not designed for diesel, Bravo 1 is the better choice, if you want that extra mph, you could try a lab finished Bravo 1 prop will give you the edge but I think your doing well as it is.
__________________
B58 is offline   Reply With Quote
Old 18 June 2015, 11:33   #10
Member
 
Country: UK - England
Town: South Coast
Boat name: Scooby Doo
Make: Arctic Blue 27
Length: 8m +
Engine: QSD 4.2 350 Diesel
Join Date: Jun 2015
Posts: 28
Thanks for the replies, consensus from the states seems to be stick with the Bravo 1. A Mirage Pro 29P may give 2 knots more top end but will suffer everywhere else.
As B58 said, perhaps during the winter I'll get the prop lab finished and see what difference it makes.

So it’s another Bravo 1 as a spare then..................better start saving!
__________________

__________________
Scooby Doo is offline   Reply With Quote
Reply

Tags
rib

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 13:52.


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