Outboard engine height

Matspain · 03 July 2016, 17:48

Hi guys
I'm new to this so I hope I've posted in the right place.
Anyway I've recently got a 4m valiant rib and a mate gave me a 40hp Johnson 2 stroke.
Got it all set up and when I took it out on the med it will not plane.
I mean as I open up the throttle It picks up speed but then the revs max out and the rib slows.
I don't think the outboard is sitting in the water enough and starts taking air (maybe)
The ac plate is level with the water when this happens.
I have noticed the ac plate is higher than bottom of the rib but i can't drop it any more.
Help please guys as it's the summer and need to get out on the sea.
Thanks
Matt from spain

jeffstevens763@g · 03 July 2016, 18:40

You have a short shaft engine Matt for a 15 inch transom your transom will be 20 inch long shaft engine required

Matspain · 03 July 2016, 19:05

Well that's just great.
I've spent a small fortune on the outboard.Is there anyway of sorting it apart from cutting the transom which I don't really want to do?

Matspain · 03 July 2016, 19:07

What sort of boat would this engine go on just out of intrest?

Seaflyer02 · 03 July 2016, 19:12

A short shaft engine would fit possibly on a SIB.
You might be able to get something like this: -
Johnson Evinrude Extension Kit #379877 #378798 40 HP 1960s - 70s * L O O K | eBay
Good luck

Last Tango · 03 July 2016, 19:19

Quote:

Originally Posted by Matspain

Is there anyway of sorting it apart from cutting the transom which I don't really want to do?

Sorry but not an option,

jeffstevens763@g · 03 July 2016, 19:27

As tango says don't cut anything try and get a leg extension or its part ex for a long shaft.

Cheers

beamishken · 03 July 2016, 19:42

If you've got a good engine and your going to keep the boat cut the transom and go boating.
I've got a 40 yam short shaft on my little 3.6m rib and it's fine keeps the centre of gravity low and doesn't cause any problems at all
If you think you might want to upgrade the engine in the near future then maybe a bad idea to cut the transom but if the engine is likely to stay with the boat then absolutely nothing wrong with a short shaft engine on a small rib
I owned mine for 15 years and use it for all manner of things from diving to waterskiing with no problems at all
Mine runs 2"high so only dropped the transom by 3"

spartacus · 03 July 2016, 20:51

Out of interest, how is that enging secured? Only looks like the bottom two bolt holes are being used?

Get a long-shaft engine and sell in the standard shaft. Cut the transom and you'll ruin the boat. Just my tuppence worth.

beamishken · 03 July 2016, 21:54

Presumably secured with the thumb screw clamps
Can someone explain what the big problem is with cutting the transom, I don't see the issue if the engine is to remain on the boat long term
Back in the 70's & 80's many boats were built as short shafts engines up to 70hp were available as short (or more correctly standard shaft)
My pal raced a power boat with an 85 yamaha converted to short shaft to lower c of g I've been running my rib 15 years with a short shaft
The boat in the picture doesn't look like it's in the first flush of youth & the op already has an engine he's spent good money on
OK in an ideal world he would buy a long shaft but depending on budget that could be fraught with problems let alone the time it may take to find the correct engine then fit it and hope it actually works once in the water
Cutting the transom he's out on the water enjoying his boat immediately
It's a no brainer to me

matt h · 04 July 2016, 10:51

No wonder he gave it to you.as said it will only fit a 15 transom.. (not your boat) and old heavy weight like that will on fit a very limited amount of boats.. if you cut the transom you will have just hacked half the value of the rib. go and get a proper engine to suit.

spartacus · 04 July 2016, 12:40

Quote:

Originally Posted by beamishken

Presumably secured with the thumb screw clamps
Can someone explain what the big problem is with cutting the transom, I don't see the issue if the engine is to remain on the boat long term.

You potentially reduce the free-board height at the transom, and all the potential issues that are likely to arise. Insurance will probably be an issue going forward, considering the boat will now be modified.

The 40hp 2-stroke standard is still desirable or some SIBs, namely older-style Zodiacs GTs and Futuras. Sell the Evinrude and by a long-shaft outboard, job done. Either that or search out the original seller!

beamishken · 04 July 2016, 19:43

Quote:

Originally Posted by spartacus

You potentially reduce the free-board height at the transom, and all the potential issues that are likely to arise. Insurance will probably be an issue going forward, considering the boat will now be modified.

The 40hp 2-stroke standard is still desirable or some SIBs, namely older-style Zodiacs GTs and Futuras. Sell the Evinrude and by a long-shaft outboard, job done. Either that or search out the original seller!

So the only down side is a bit of loss of freeboard and potential insurance issues?
Come on ffs it's a rib you get a bit of water over the stern so you drive away and it drains out!
It's been modified is a problem? have you read some of the threads about refurbs and upgrades, people change their boats a lot more than dropping the transom a few inches and don't give it a second thought
The original seller gave him the engine so I guess no joy there!
The boat will be fine with a lowered transom.
my boat is 3.6m and has ample freeboard even loaded with 2 divers all the kit and a driver & it's never sunk, if we leave it in a marina we drop the trunk if it rains we get 50mm of water on the deck the rest runs out the trunk
I'd assume the op is on a budget seeing as he was given the engine so his most cost effective way to go boating is chop the transom a bit of glass over it & go boating
Even if he wants to fit a long shaft later it's not a massive job to rebuild just look at all the Sr 4 rebuild threads almost every one has replaced the transom

spartacus · 04 July 2016, 20:45

Quote:

Originally Posted by beamishken

Come on ffs it's a rib you get a bit of water over the stern so you drive away and it drains out! It's been modified is a problem? have you read some of the threads about refurbs and upgrades, people change their boats a lot more than dropping the transom a few inches and don't give it a second thought.

Considering the OP bought the outfit, not fully understanding that the engine wasn't right speaks volumes. What's he going to do, take out his junior hacksaw?

Quote:

Originally Posted by beamishken

The original seller gave him the engine so I guess no joy there!
The boat will be fine with a lowered transom. My boat is 3.6m and has ample freeboard even loaded with 2 divers all the kit and a driver it's never sunk if we leave it in a marina we drop the trunk if it rains we get 50mm of water on the deck the rest runs out the trunk.

I don't doubt it will be fine. That's just my opinion.

two stroke mick · 04 July 2016, 20:47

Would a four blade prop help with this problem. And yes know that the shaft length should be long and not the short shaft on. Just a thought
Tsm

Matspain · 04 July 2016, 20:54

Thanks for the information guys.
I've had nothing but problems with this rib.
The rib is great but came with a 13.5hp which was boring obviously.
Found this 40hp which was sat in an under build and possibly for years.Even though it looks tatty the mechanic says it's done hardly any work and the compression is spot on.I had to buy new throttle control box etc and after that it still doesn't go like I thought it would.Gutted really as this has taken months to sort out.
Don't want to cut the transom so will just potter around till something else turns up.
Do you guys think this motor would fit on an old fletcher arrow because I know someone selling and it's probably cheaper and easier than finding a new outboard.
Thanks again

Matspain · 04 July 2016, 20:56

This is the boat I could buy. Are they any good and would the motor fit it?
Thanks again

Matspain · 04 July 2016, 21:03

And yes I'm very new to boats (this is my first )and I'm learning quickly through my stupid mistakes😤

beamishken · 04 July 2016, 21:20

I don't see your reasoning in buying another hull to fit the engine to,when you have the answer for almost no cost?
A Fletcher may be a short shaft transom but will almost certainly be inferior to the rib you already have
why not alter the rib to fit the engine at zero cost and go boating?
If you get the jigsaw or grinder out you could be on the water in a couple of hours instead of searching adverts for a hull to fit the engine or an engine to fit the hull
Surely the answer is marry together what you have?

Matspain · 04 July 2016, 21:38

It does sound tempting.
I'm more than capable of doing it but would it weaken the transom?
This motor must be 150kg+