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Old 09 September 2019, 16:03   #1
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Country: UK - Scotland
Town: Aberdeen
Boat name: QuickSilver
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Length: under 3m
Engine: Tohatsu 5Hp
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My boat don't plane

Hi everyone

I have a 2.5m airdeck Mercury Quicksilver ( 28kg ) and a 4stroke Tohatsu 5Hp ( 28kg ) short shaft

Can't get on plane

I have done this:

0. I have inflate all compartments at the prescribed pressure including the airdeck.

1. changed different trim positions even the first one closest to the transom

2. moved myself in different positions including towards the bow and even on top of the bow.

3. start very slowly and increased gradually the rev

4. start with a high rev

No matter what I do the engine digging in the water immersing the transom and raising the bow.

I give up as yesterday I have spent almost 2h on the sea and constantly doing adjustments but getting the same results.

If anyone can throw some advise would be much appreciated

Thank you advance guys for your time to read this and eventually for any future involvement in solving this unpleasant situation

Respectfully

Manus
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Old 09 September 2019, 16:29   #2
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Country: UK - England
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Boat name: Nimrod II
Make: Aerotec 380
Length: 3m +
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Hi Manus and welcome to the forum.

Many small SIBs can plane one-up with no extra weight of kit using a 5hp but sometimes a SIB nearer 3m than 2.5m is actually better.

The only thing I can think of is... have you tested the pressures... floor in particular... after it's been sitting on the water 5 mins... is the outboard making its full revs... what is the prop pitch... and is the outboard shaft length correct for the transom?

David
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Old 09 September 2019, 17:07   #3
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Country: UK - Scotland
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Engine: Tohatsu 5Hp
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Quote:
Originally Posted by Fenlander View Post
Hi Manus and welcome to the forum.

Many small SIBs can plane one-up with no extra weight of kit using a 5hp but sometimes a SIB nearer 3m than 2.5m is actually better.

The only thing I can think of is... have you tested the pressures... floor in particular... after it's been sitting on the water 5 mins... is the outboard making its full revs... what is the prop pitch... and is the outboard shaft length correct for the transom?

David
Thank you David for your message.
Yes the floor is it at his recommended pressure.
The outboard is brand new so is the boat and yes the engine is short shaft as recommended by the boat manufacturer, max 30kg and 5hp
I had another 2.3m inflatable before which went on plane at less that 50% of the rev using a smaller 3.5hp mariner
And yes is it only myself onboard with no any additional gear .
Iím so confused
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Old 09 September 2019, 23:00   #4
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Country: UK - England
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Donít know much about SIBs but the chance of planing with 5hp must be very slim, it surely must be down to total weight at that level. What the OP hasnít told us is what weight is he/she because all due respect we could come up with suggestions forever and as an example if he/she is 20 stone it is never going to happen.
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Old 10 September 2019, 01:17   #5
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Country: UK - Scotland
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Yes good point 😀
Iím 14 stones.
The idea is that I was going on plane with my previous inflatable using a 3.5hp 🙈
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Old 10 September 2019, 01:32   #6
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That's a horribly weightly lump on the back of a very short SIB - many of us use the 15hp Merc/Mariner 2 stroke and that is only another 8 kg or so for three times the power.

As others have said - short boat+ underpowered/overweight engine + poor weight distribution = a struggle!

Presuming the engine is performing correctly and not trimmed right out or something.
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Old 10 September 2019, 03:13   #7
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Quote:
Originally Posted by Manus View Post
Hi everyone



I have a 2.5m airdeck Mercury Quicksilver ( 28kg ) and a 4stroke Tohatsu 5Hp ( 28kg ) short shaft



Can't get on plane



I have done this:



0. I have inflate all compartments at the prescribed pressure including the airdeck.



1. changed different trim positions even the first one closest to the transom



2. moved myself in different positions including towards the bow and even on top of the bow.



3. start very slowly and increased gradually the rev



4. start with a high rev



No matter what I do the engine digging in the water immersing the transom and raising the bow.



I give up as yesterday I have spent almost 2h on the sea and constantly doing adjustments but getting the same results.



If anyone can throw some advise would be much appreciated



Thank you advance guys for your time to read this and eventually for any future involvement in solving this unpleasant situation



Respectfully



Manus
Not enough power mate !
I have a 2.6 rib tender fibre glass hull and tubes with a two stroke tahatsui 9.8 with a tiller extension on throttle so i can lay forward
And i have put a bit off wood on transom to higher prop as to low it does 30knts on my own will not plain with two adults
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Old 10 September 2019, 03:16   #8
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Quote:
Originally Posted by carldalmas View Post
Not enough power mate !
I have a 2.6 rib tender fibre glass hull and tubes with a two stroke tahatsui 9.8 with a tiller extension on throttle so i can lay forward
And i have put a bit off wood on transom to higher prop as to low it does 30knts on my own will not plain with two adults
Engine wieghs 35kilos
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Old 10 September 2019, 03:22   #9
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Country: UK - England
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OK so at 14st and no other kit... and knowing you could plane with a 3.5hp... plus you've tried altering weight distribution and know pressures are OK I can only think you need to try a lower pitch prop. The Mainer 3.5hp may have had a lower pitch prop enabling it to be in a better part of the power band at the point it was climbing onto the plane.

It would be interesting if you bought a £10 rev counter/tach to know what revs you are getting to flat out but not on the plane.

With a 5hp supposedly modded to 6hp and a 2.85m Zodiac with two adults this planes well...



And a Tohatsu 5hp easily getting a 3.2m on the plane...

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Old 10 September 2019, 03:29   #10
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Country: UK - England
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Have a look at the prop Manus and let us know the pitch or part number markings.
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