Reply
 
Thread Tools Search this Thread
 
Old 13 August 2011, 02:33   #11
Member
 
Country: Other
Town: Rosas
Boat name: Conqueror
Make: Valiant
Length: 7m +
Engine: Outboard 150hp Merc
Join Date: Dec 2010
Posts: 541
Send a message via Skype™ to Courageous
One further question - is 3k about the right revs to set before I try to trim to find the grip or would you use a different figure? I suppose it's dependant on individual circumstances is it?
__________________

__________________
Courageous is offline   Reply With Quote
Old 13 August 2011, 05:23   #12
RIBnet supporter
 
Pikey Dave's Avatar
 
Country: UK - England
Town: South Yorks
Boat name: Black Pig
Make: Ribcraft
Length: 5m +
Engine: DF140a
MMSI: 235111389
Join Date: Feb 2008
Posts: 7,596
RIBase
I'm not sure about your 3k rpm to "find Grip" Does your prop have vent holes in it? these are holes drilled into the hub around the circumference at the gearbox end (as opposed to the prop nut end) From astanding start you would normally trim all the way down, apply the throttle & get the boat moving & planing. Once she is planing, start to trim up until the prop cavitates & trim back in slightly. Trim in on tight turns. I had similar problems to you but for different reasons, 4 blade props (rev 4's) made a huge difference. Even now, if I try & set off with the engines trimmed out, I just sit there & "wheelspin"
__________________
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5
Pikey Dave is offline   Reply With Quote
Old 13 August 2011, 05:37   #13
Member
 
The Grocer's Avatar
 
Country: UK - Scotland
Town: Kildonan, Arran
Boat name: Cowal (& Bennan)
Make: Quinquari Humber/RC
Length: 6m +
Engine: Suzuki DF150/DF175x2
MMSI: 235036953
Join Date: Jun 2006
Posts: 296
Quote:
Originally Posted by Courageous View Post
One further question - is 3k about the right revs to set before I try to trim to find the grip or would you use a different figure? I suppose it's dependant on individual circumstances is it?
How do I do it? I can feel (and see) the bow rising as I accelerate, leaving the trim alone; then the boat levels as it gets "over the hump" and onto the plane. This when I start to trim out; a little at a time to let the boat settle; the boat should accelerate more without additional throttle as the drag is reduced. Eventually no more benefit is gained or the boat slows - trim in a touch and enjoy the ride!

(Turning: big wide turns - leave the trim alone, probably; tight, fast turns - trim in to prevent loss of hull grip and/or ventilation).

There are people on here who know far more than I do; and if you haven't already I can recommend the RYA powerboat courses.

Each boat will vary, and each journey will be different; and as loads change through the day so the settings will change. The dials and numbers on the console are only guides - as you get to know your boat you will feel what the right settings are for each occasion. This is part of the fun of driving a fast boat...
__________________
Russell
The Grocer is offline   Reply With Quote
Old 13 August 2011, 05:54   #14
Member
 
Country: Other
Town: Rosas
Boat name: Conqueror
Make: Valiant
Length: 7m +
Engine: Outboard 150hp Merc
Join Date: Dec 2010
Posts: 541
Send a message via Skype™ to Courageous
Thanx Russ that's great advice -These are great fun but I'm still a yottie at heart........

Ducks for cover!
__________________
Courageous is offline   Reply With Quote
Old 13 August 2011, 08:05   #15
Member
 
Oscarguitar's Avatar
 
Country: UK - England
Town: Poole
Boat name: Half Cut
Make: Cobra 8.6
Length: 8m +
Engine: Verado 275
MMSI: 235104619
Join Date: Jun 2011
Posts: 378
If your cav plate is just visible you don't not need the extention. It there anything mounted on the transom near the prop? Transducer or something? Even a small obstruction can disrupt the flow over the prop especially when getting onto the plane. If you have anything in the way it can make a big difference. You said the previous owner had an XL but that may have been to overcome a problem that could be solved more efficiently.

Adding the extention will drop your prop another 5" that is going to create massive drag, reduce speed and increase consumption. You really should try a different prop before you bolt that thing on. Try and borrow one from someone.

Technique wise, I have always trimmed right in, throttle up and once on the plane trim to suit.
__________________
Oscarguitar is offline   Reply With Quote
Old 13 August 2011, 21:24   #16
Member
 
Country: Other
Town: Rosas
Boat name: Conqueror
Make: Valiant
Length: 7m +
Engine: Outboard 150hp Merc
Join Date: Dec 2010
Posts: 541
Send a message via Skype™ to Courageous
Thanx Oscar. Valiant state that a single motor must be XL. Twins can be L. I just didn't check that before buying the replacement.........

The little thing in front of the prop is the skeg! 25 inch transom and 20 inch leg doesn't quite work does it? You mentioned before that I am experiencing 46% slip or thereabouts. The boat is a standard DR750, the prop is a standard 3 bladed lazer in good nick - surely that only leaves leg length no?
__________________
Courageous is offline   Reply With Quote
Old 14 August 2011, 06:06   #17
RIBnet admin team
 
willk's Avatar
 
Country: Ireland
Make: Redbay Boats
Length: 9m +
Engine: 370hp
Join Date: Feb 2008
Posts: 12,928
RIBase
It's the leg length not the prop, although a higher pitch might reduce the ventilation.

I have a gut feeling (no facts, sry) that having a 150hp may be making the problem worse - it's at the lower end of acceptable power for this size of boat. Valiant show it as the recommended HP, but list 115-300 as the useable range. That's a bit of a crowd pleaser. Most users on here would be starting at 200hp or more for that RIB.

In any case, you have committed yourself to action (leg extension) and until then you're going to have to keep your trim down.

Anyhoo, there's my last call for boarding - gotta dash - just time for a last quick one at the bar...

__________________
willk is online now   Reply With Quote
Old 14 August 2011, 07:03   #18
Member
 
longjohn's Avatar
 
Country: UK - England
Town: Bournemouth
Boat name: Seadrive
Make: Capelli Tempest 470
Length: 4m +
Engine: Suzuki DF70
MMSI: 235079113
Join Date: Jul 2008
Posts: 541
Rib Magazine tested this combo (Merc 150) and stated 50mph was attainable - sounds very optimistic to me - no mention of shaft length tho!
RIB Magazine - Rigid Inflatable Boats, RIB Boats - RIB International Ltd - Valiant DR 750

Also interesting that the Valiant brochure shows shots of a DR750 with Merc 175 & 200's and definitely states XL for a single motor installation

John
__________________
longjohn is offline   Reply With Quote
Old 14 August 2011, 07:24   #19
Member
 
Country: Other
Town: Rosas
Boat name: Conqueror
Make: Valiant
Length: 7m +
Engine: Outboard 150hp Merc
Join Date: Dec 2010
Posts: 541
Send a message via Skype™ to Courageous
Ya right Will. I am looking for a replacement as we think it's pertinent for a business to have a spare. I was interested in going down to a 135 but with your advice I'll edge towards the 200-225 I think.

Thanx for the linky to the article John, will download it now and take a gander when I'm at work this avvy!

Cheers guys!
__________________
Courageous is offline   Reply With Quote
Old 14 August 2011, 07:26   #20
RIBnet admin team
 
willk's Avatar
 
Country: Ireland
Make: Redbay Boats
Length: 9m +
Engine: 370hp
Join Date: Feb 2008
Posts: 12,928
RIBase
Quote:
Originally Posted by longjohn View Post
Rib Magazine tested this combo (Merc 150) and stated 50mph was attainable - sounds very optimistic to me
HMS's statistics tend to be, um, a little hazy
__________________

__________________
willk is online now   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 06:42.


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