Reply
 
Thread Tools Search this Thread
 
Old 02 June 2014, 08:11   #11
Member
 
Country: UK - England
Town: Dorset & Hants
Boat name: Streaker/Orange
Make: Avon/Ribcraft
Length: 4m +
Engine: 50Yam/25 Mariner
Join Date: Apr 2007
Posts: 5,551
I'm running a 25 hp 4 stroke on a 3.6m rib.

I just think your asking/expecting too much of 20hp.
__________________

__________________
PeterM is offline   Reply With Quote
Old 02 June 2014, 12:01   #12
Member
 
Locozodiac's Avatar
 
Country: Other
Town: Lima-Peru
Boat name: Nautile
Make: Sea Rider Boats
Length: 4m +
Engine: Tohatsu 18 /30 HP
Join Date: Sep 2007
Posts: 1,706
My 430 rib with just a 18 HP tuned to perfection with 3 adults planes easily on most sea conditions. Unless you have a built in tach inside yoiur ear get a physical one, are cheap, will make your boating day.

If you're lost not knowing where to start rigging a small sib/rib with a 20 HP check this : + add an induction tach

ABC Sib-Rib Installation Guidelines.-

Happy Boating
__________________

__________________
Locozodiac is offline   Reply With Quote
Old 02 June 2014, 15:53   #13
RIBnet admin team
 
Poly's Avatar
 
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: 2 stroke YAM 20 HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 10,114
Quote:
Originally Posted by Northsearibber View Post
Engine is a Yamaha f20 2013. Prop size is 9.25 x12.Speed - would have to let you know exactly but about 12/13 mph.
OK - Yamaha says your engine max rpm is 5000-6000 rpm. With a 2.08 gear ratio. So at 5000 rpm your prop should be spinning 2400 times per minute. Assuming no slip that would mean your prop moves forward 12x2400" a minute = 23.7 knots. Bearing in mind that 10% slip is about the best you will get you should be getting 20ish knots (23 mph). On a small boat it feels like more. You think you are only getting 1/2 that - so I think there is a problem.

Is it sitting bow up?
Is it generating a huge wake behind it?

Its going to take actual tacho and speed data to work out more - and ideally some video footage so people can see how she is sitting.


Quote:
Originally Posted by PeterM View Post
I'm running a 25 hp 4 stroke on a 3.6m rib.

I just think your asking/expecting too much of 20hp.
I'm running a 20 HP 2-str on a 3.9m and think he's not!
__________________
Poly is offline   Reply With Quote
Old 02 June 2014, 20:01   #14
Member
 
Country: Canada
Town: Trois-Rivieres
Length: 3m +
Join Date: Jun 2014
Posts: 2
I have a Brig 360 with the same engine (2013 Yamaha 20 HP 4 strokes). Two adults and three kids (total weight around 200 Kg) I get 25 mph with a 9 1/4 x 10 propeller. When I tow a large 3 persons towable tube with the three kids on it I get 20 mph with a 9 1/4 x 9 propeller. I never had problem to get on plane. I think your engine is appropriate for the size of your rib, you just have to find a good setup.

Dominic
Quebec, Canada
__________________
dvoyer is offline   Reply With Quote
Old 03 June 2014, 12:06   #15
Member
 
Country: UK - England
Town: wetherby
Boat name: s
Make: ribeye
Length: 3m +
Engine: outboard
Join Date: Oct 2012
Posts: 8
Thanks guys - all those comments are really useful and have been a lot of help.

The general opinion seems to be that boat/engine combo should be capable of 20 mph with a couple of adults on plus 1 maybe two kids. That is what I am after really so it seems the issue is in the set up . I have ordered a induction tach and with advice given will do a few tests when I next get the rib out - hopefully next weekend. Hopefully I will be able to sort the issue now but I may need more views and advice! Either way I will repost with some results

Again - many thanks to all who have offered the benefit of their experience

Cheers for now!
__________________

__________________
Northsearibber 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.