2.5hp vs 5hp flat bottom inflatable

[Disschord]

Hi I was speaking to an outboard dealer as I was considering upgrading from a 2.5hp to a 5 or 6 hp for my 2.6m flat bottom slatted floor inflatable.
The dealer told me I should not expect any noticeable speed improvement because I am limited by the hull shape and I am probably at or close to the max speed for the displacement hull shape.

It was nice of the dealer not to just rip the money out of my hand but what are you opinions on this?

[Nick Hearne]

I would agree, as you are not going to be able to get on the plane with the flat bottom! If you want to go faster chop it in and buy a new second hand rig

[apshutt]

I would also agree with both the dealer and Nick the extra weight would keep the speed increase down. Do not imagine that double the power means double the speed. Having said that your 2.5hp engine would not push a V floor faster than the flat floor. So as suggested a rethink of your set up would be the better option.

[The Gurnard]

The bigger engine will just push a bigger bow wave in front of your slat floor boat.. and give a bigger wake at the rear end.. with just a little speed increase.. its just the nature of displacement type boats.. and I know from my 2.7m slat floors performance with various size small outboards

however if an outboard was big enough to push it over the top of the bow wave ..and get it to plane .. and perhaps a 5hp or 6hp two stroke could do that.. it would be much faster.. but it would have little directionally stability .. Its much like throwing a skipping stone across water

as the others mention.. you need to think of a different type of hull if you want go fast and have stability

[Searider]

Really???????

Depends on your weight.

When I was a teenager we mucked about with all sorts of tenders.
Avon Redstart with 2hp Evinrude planes with 9 stone.
GB280 planes very well with 2.2hp Mercury. Went even better with the restrictor out releasing the full 3.3hp!
2.8m Humber went very well with 7.5hp Mercury longshaft!

My lads current boat an Avon RAB3.15 - which has the roll up plastic floor planes with a 4hp. The floor does seem to be a bit wavy though!

[solent spence]

In my much younger days, and with careful positioning, I could get an Avon redstart on the plane with a 4hp evinrude (the 70's version with the horizontal sliding throttle on the front), but it didn't like it and would become a bendy mess easily.

Happy days though

[Disschord]

Would replacing the slated floor with a single piece of ply help my ability to plane?

[The Gurnard]

Sorry guys ..Guess Im just making it up .. and the dealer didn’t really want to sell an engine

Here is real photo My avon redstart with a Yamaha 2hp engine.. and even when I was a kid..it wouldn’t plane with one on board.


Here is my 2.7 seago slat floor with 3.3hp flat out.. its making a big wake but I can assure you..its all foam and its not on the plane. Sorry I don’t have a photo of it with my Tohatsu 4hp four stroke ..I did use it once to try but it was no better than the 3.3hp.

However Im almost 13 stone so perhaps its cos Im could be considered a fat barsteward that I cant get small SIBS to plane with small outboards.



Has any one got any photos to show an avon redcrest on the plane with a 2 Hp engine to illustrate these amazing feats of fastness ?
On my redstart its little wooden transom folds with the 3.3hp under full power..but its getting quite old now (the boat..the engine is still great and a 2005 one)

Disccord..I made a solid full piece floor for my wee avon redstart..and nope it doesn’t go any faster..but it sure makes it easier to get in and out of. I couldn’t honestly comment on a solid floor on a larger slat floor though..I have no experience of that.

[Disschord]

Thanks gurnard your post is great and my mind is made up

I'm sticking with the 2.5hp and flat bottom boat.
Maybe in a few years I will upgrade the whole rig

Thanks for all your replies

[The Gurnard]

Disschord

I love my seago slat floor and the Suzi 2.5hp four stroke. Its so easy to roll up..throw in the car ..then in the shed..its not been looked after ..but its around 14 years old..and still going strong. I wont part with it and its still used regular.

The redstart..its almost retired now..although I do use it as a tender if I moor my larger boats off shore.

Obviously I have to watch the weather on the Seago..but I do go out to sea in it and have done journeys like circumnavigate the Island of Gigha in it. Its been full to the gunnels with fish too

You can have a lot of fun in any boat

[kaman]

My mate had a 2.7 m air floor Chinese made Sib with a 4 hp yamaha 2 stroke engine on the back.
He is a 11 stone.
He always maintained it could and did plane.
I can vouch for this having seen it planing once.
However most of the time it was bow up in the air and a big displacement wake.
If your going to get a Sib that planes best get one that does it with ease.

[Nos4r2]

I've got a Seago with inflatable floor and a Yam 8hp 2 stroke. It planes quite well with me aboard and I'm a fat git.

It very nearly planes with me and Sixy in it, so would probably be ok with 2 'normal' people in it.

However, I do have a vid of a small airfloor dinghy planing from a good few years ago with my 2.2hp on it. Not saying who's at the helm but it's not me!

https://www.youtube.com/watch?v=fmLZ9VxCnP4

[The Gurnard]

Quick question Nos4rs.. are your inflatable floors completely flat on the bottom..or do they have a little profile..like a small keel shape or a little bow shape ?

If so.. then perhaps we are discussing a different design boat from a slat floor.

Im fully aware small inflatables with air floors that have little keels and a sloping front plane without any difficulty..but Disschord specifically mentioned a flat floor..and slats

[Disschord]

Here is my setup

[Nick Hearne]

OK I may be wrong but I still would sell what you have and buy a good used inflatable with a keel and a 2st outboard if you want to go faster.
I had a flat bottomed inflatable Yam with a Yami Malta and that was sloooooow !

[The Gurnard]

Found this on U Tube Disschord ..a 6HP Suzuki powering what looks like a slat floor boat..as opposed to an airdeck floor.. which is a totally different hull shape.

He tries his best to get it over the bow wave..but its just not going to happen..for him..although his engine might need a wee bit of trimming

https://www.youtube.com/watch?v=EWJ_5T_JUJw

If that suits you..go for it

[Disschord]

Thanks for all your help everyone. I don't have the money at the moment to upgrade both the engine and the boat so I am going to do a little saving and hopefully upgrade both next year.