Reply
 
Thread Tools Search this Thread
 
Old 10 September 2019, 06:29   #11
Member
 
Manus's Avatar
 
Country: UK - Scotland
Town: Aberdeen
Boat name: QuickSilver
Make: Mercury
Length: under 3m
Engine: Tohatsu 5Hp
Join Date: Sep 2019
Posts: 6
Is the default propeller that comes with the outboard.
7.8 diam and 8 pitch
__________________

__________________
Manus is offline   Reply With Quote
Old 10 September 2019, 07:04   #12
Member
 
Country: UK - England
Town: Cheltenham
Boat name: Mavi Su
Make: Cobra Nautique 6.6
Length: 6m +
Engine: 150
MMSI: 235114058
Join Date: Oct 2011
Posts: 233
RIBase
I suspect you need a more powerful motor - you might get your 14 stones on the plane with a new prop, but once you add a picnic and some gear you may not be able to plane. i suspect the choice is 1. be happy and wet at displacement speeds or 2. buy a new outboard.
__________________

__________________
You Can't cross an Ocean unless you have lost site of shore.
charliee is offline   Reply With Quote
Old 10 September 2019, 07:19   #13
Member
 
Country: UK - England
Town: East Anglia
Boat name: Nimrod II
Make: Aerotec 380
Length: 3m +
Engine: Yamaha 15Hp 2-stroke
Join Date: Nov 2007
Posts: 4,953
Hmm well gut feeling is the 8" may be too much and not allowing the OB to get into the powerband where it's able to push it over the hump onto the plane.

The standard pitch for many 15hp motors was always only one pitch up at 9" and they had triple the power to spin that pitch.

I've known folks with 6hp motors drop down to a 7" with a useful improvement in their ability to plane.
__________________
Fenlander is offline   Reply With Quote
Old 10 September 2019, 08:14   #14
Member
 
The Gurnard's Avatar
 
Country: UK - Scotland
Town: Stirling
Boat name: The Gurnard
Make: Quicksilver
Length: 4m +
Engine: mariner 25hp 2s
Join Date: Jul 2013
Posts: 1,260
Hi Manus ..Fenlander is bang on the button as usual...with his suggestion to try a smaller prop

I did a recent test with a Honwave T38 airfloor as a couple of guys I know asked if it would plane with a 6HP. I said it would..most said..no chance !!!

I borrowed the boat and put my standard Yamaha 6HP four stroke on it and within a couple of meters she was happily on the plan. (I give the thumps up in the video when it goes on the plane.. around 10 meters after starting.)

It gave similar performance as my wee F Rib 2.75 with the outboard..example planed easily and went approx 15mph. I weigh 200lb ..so much same as yourself. The boat was empty except transom wheels..big bow dodger ..front seat and 10 litres of fuel.



The owner then tried and he struggled to get it on the plane. He weighs 50lb more than me. It did get on the plane after a long run but we could both see it was struggling and it was in fact labouring the outboard. I put a smaller prop on and he tried again. This time he got much the same performance as myself except he could only reach around 12 mph top speed.

For info..the prop I used for myself with the 6HP is the bog standard 7.1/4 x 8” pitch. It was running at 5150 revs to give me around 15 mph tops. (Max recommended is 5500 for my OB) The smaller pitch that gave my friend better performance was a 7.1/2 x 7” pitch and it too reached good revs with the smaller prop.

You are using an 8” pitch on a 5HP ..so you should get better performance with a 7” pitch but not as good a top speed. But as others have said.. it will be marginal performance and as soon as you get a few fish on board..it possibly wont plane the way it did on the way to get the fish.

Im pretty certain you will get it on the plane with trial and error and perhaps the smaller prop..but it could well be a bit disappointing with its performance.. however that is entirely up to you if all you want is to get it to plane with nothing else on board..
__________________
The Gurnard is offline   Reply With Quote
Old 10 September 2019, 08:22   #15
Member
 
Manus's Avatar
 
Country: UK - Scotland
Town: Aberdeen
Boat name: QuickSilver
Make: Mercury
Length: under 3m
Engine: Tohatsu 5Hp
Join Date: Sep 2019
Posts: 6
Guys

Thank you so much for your replies, Iím so grateful 😀

Everything you are saying make sense .........but still one aspect haunting me

How was possible to get on plane with my previous 2.3m inflatable using a 3.5hp mariner ????? And now Iím not capable 🙈
__________________
Manus is offline   Reply With Quote
Old 10 September 2019, 08:42   #16
Member
 
The Gurnard's Avatar
 
Country: UK - Scotland
Town: Stirling
Boat name: The Gurnard
Make: Quicksilver
Length: 4m +
Engine: mariner 25hp 2s
Join Date: Jul 2013
Posts: 1,260
Hi again Manus Im afraid only you will know the answer to that one.

Here is some of my trials and results

FRib 2.75 empty boat will plane with a 3.3HP ..put anything else in boat example anchors and other essential stuff it wont plane.It easily planes with a 6HP and all my gear for a day

Seago slatfloor 2.7 planed with a borrowed 5HP but skittered around as it was a slatfloor so I didn’t do it often. It would not plane with a 3.3HP

Lodestar 3.2 airfloor easily planed with a 6HP would not plane with a 3.3HP
I have no experience of trying to plane a 2.5 with a 5HP or a 2.3 with a 3.5HP, so cant help you.


Totally irrelevant. But my 4.3m SIB easily planes myself and two other adults with its 25HP. With another adult it wont plane..yet I have heard some folk say they get them to plane with 7 folks on board.
__________________
The Gurnard is offline   Reply With Quote
Old 10 September 2019, 09:40   #17
Member
 
Country: UK - England
Town: East Anglia
Boat name: Nimrod II
Make: Aerotec 380
Length: 3m +
Engine: Yamaha 15Hp 2-stroke
Join Date: Nov 2007
Posts: 4,953
>>>How was possible to get on plane with my previous 2.3m inflatable using a 3.5hp mariner ????? And now I’m not capable ��

First many thanks to The Gurnard for his real life experience demonstrating in marginal power situations prop pitch is important and just one inch can make a big difference.

Why was it OK with the 3.5 Mariner? Well I'm taking a guess it had a lower pitch prop so allowing it to get into its peak power range at the point it needed to overcome resistance and plane.

My gut feeling is the 5hp is being bogged down by that 8" just before it reaches the power band it needs to get onto the plane.

A £10 tach may give a clue if you want to try that and report back the revs you are seeing... other than that it's taking a chance on a new prop around £75 from Tohatsu.

If you do take the plunge with a new prop be cautioned only a genuine Tohatsu 7" can be assured to behave as 1" pitch lower than yours. Some aftermarket brands are inaccurately pitched or have a slightly different design that causes them to behave differently.

Of course in marginal power outboard situations nothing is guaranteed so we can only give best advice and hope it works out.
__________________
Fenlander is offline   Reply With Quote
Old 10 September 2019, 16:51   #18
Member
 
Country: Australia
Town: Dalmeny
Make: zodiac
Length: 5m +
Engine: outboard
Join Date: May 2015
Posts: 914
Just checking, what length outboard is the latest one, a short shaft as the name mentions doesn't sit as deep causing as much drag. The plate just above the prop should be close to level with the bottom of the hull. Next thing as a few have mentioned is prop, or should I say prop pitch. Reducing pitch will give a faster execration which sounds like what's needed to get this little boat out of the hole its digging as you open it full throttle. If like you say the bum is burying in and the bow rising, the engine should be trimmed in further.

On a larger boat a set of trim tabs would greatly help give lift at the back end. If it was me I would be looking around my garage for a couple of suitable L shaped brackets I could cut and fix to the stern to create the same effect of trim tabs, these wouldn't need to be very big at all to give extra lift on such a small vessel.
__________________

__________________
jonp 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 09:27.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.