New engine height

sburt10 · 29 October 2011, 11:17

My mate is mounting a new engine on his new rib, any tips on how to work out the engine height ?

Its a 5.2 m rib with a long shaft engine on a 20" transom.

Sea Witch · 29 October 2011, 14:07

Short shaft is wat u need , only way out is fibre glass 5 " to top of transom or buy a jack plate

willk · 29 October 2011, 14:19

I think Sea Witch may have misread your post. Your mate has the right engine length. General recommendation is to have the anti-ventilation plate level with or slightly below the bottom of the transom when in a neutral trim position.

I suppose there are more accurate specs for a particular hull/engine/load/prop combination. If you state RIB type and engine model, I'm sure someone on here will have tried it.

Boats&Outboards · 29 October 2011, 14:20

No you don't need a short shaft as they are on 15in and won't reach!!!

The new motor should come with a transom template which can be used to drill the locating holes for the first time.

Shaft lengths are confusing now on new motors as most new sales refer to a standard shaft being the 21 inch model with the 25in shaft now known as the long. Most people are used to the older system, when told long assume it to be 21in and call the 25in an XL.

Not that it matters as you have the engine it's just your trying to find where exactly to bolt it onto the transom ?

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

willk · 29 October 2011, 15:39

Quote:

Originally Posted by Boats&Outboards

Shaft lengths are confusing now on new motors as most new sales refer to a standard shaft being the 21 inch model with the 25in shaft now known as the long.

Outboard manufacturers still use Short, Long and Extra Long or refer to the Transom depth in inches, 15", 20", 25". I've never seen Manufacturer specs referring to a "Standard" Shaft. It's dealers who use confusing terminology.

Long is 20", not 21".

Boats&Outboards · 29 October 2011, 17:53

Quote:

Originally Posted by willk

Outboard manufacturers still use Short, Long and Extra Long or refer to the Transom depth in inches, 15", 20", 25". I've never seen Manufacturer specs referring to a "Standard" Shaft. It's dealers who use confusing terminology.

Long is 20", not 21".

That's my point, new retail sales, not the manufacturer. your right the builder refers to the transom height but th dealer the "shaft length"

Long "shaft" is 21 inches to fit a 20 inch transom giving the facility to fit it "off the transom" Measure your "long shaft" I bet it's 21 inches to the cav plate

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

willk · 29 October 2011, 18:51

Quote:

Originally Posted by Boats&Outboards

Measure your "long shaft" I bet it's 21 inches to the cav plate

No, the Long I have to hand is almost 23", the Short one is 17". They're generally referred to by the intended transom length, not the actual measurement of the motor.

Your eBay page has me even more confused:
"short shafts are around 15 inches, Standard outboards are around 18 inches and the long are around 23 inches. You measure the outboard length from the outboard's bracket that sits on the boats transom to the cavitation plate just above the prop as shown below. Easy as that right ?? wrong, be careful, standard shaft is often referred to as short shaft and vice versa. To confuse things more there are some boats that require an extra long shaft, normally around 25 inches, these were made simply to confuse you, no ok there of course serve a purpose for larger transoms but are very rare and hard to obtain"

If you need any very rare 25" motors, I'm sure I could scout a few for you...

Boats&Outboards · 29 October 2011, 18:55

That was written a very long time ago and is out of date at a time when an XL shaft was not the "norm". It relates to smaller engines.

Thanks for the heads up I'll edit it.

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

sburt10 · 29 October 2011, 22:30

Hi Boats and Outboards, yes, the bolt hole is what I am after help with. The RIB was brand new and had never been in the water however it did have an outboard fitted but never used so the holes are all there, its just a guide as to where the cav plate should sit I guess.

C-NUMB · 29 October 2011, 22:34

Would recommend to check the distance to cav plate before drilling in any case. As an example, 25 hp Tohatsu, differenced between 25 hp 2 stroke and 4 stroke (short leg) engines is 1.2 inch...

2STROKE/Dimensions
Short rig, distance to cav plate is 17,1

TLDI/Dimensions
Short rig, distance to cav plate is 15,9 inch

Boats&Outboards · 29 October 2011, 23:00

Quote:

Originally Posted by sburt10

Hi Boats and Outboards, yes, the bolt hole is what I am after help with. The RIB was brand new and had never been in the water however it did have an outboard fitted but never used so the holes are all there, its just a guide as to where the cav plate should sit I guess.

If your unsure place yours on the transom using temporary bolt (it should sit just above the transom and not actually be resting on it) and see if they all line up (don't drill new ones or secure it just yet). Then check the cav plate is sitting lever or at very most 1 inch under the bottom of the transom.

What size of engine was fitted before, what size are you fitting ?

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

sburt10 · 30 October 2011, 06:48

Quote:

Originally Posted by Boats&Outboards

If your unsure place yours on the transom using temporary bolt (it should sit just above the transom and not actually be resting on it) and see if they all line up (don't drill new ones or secure it just yet). Then check the cav plate is sitting lever or at very most 1 inch under the bottom of the transom.

What size of engine was fitted before, what size are you fitting ?

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

Keeping it simple, a 90 mariner was fitter and we are putting a 90 merc on so the holes should all up ok.

Courageous · 30 October 2011, 09:24

Assuming it was set up properly originally it strikes me you are all having a conversation about precisely "nothing".........

sburt10 · 30 October 2011, 09:32

Quote:

Originally Posted by Courageous

Assuming it was set up properly originally it strikes me you are all having a conversation about precisely "nothing".........

No, there are several different holes on an outboard bracket to allow you to adjust the height, the wrong height of the engine can affect performance a lot We would like to get as close to correct as possible as lifting a 170kg engine after it has been mounted is a pain, as is a poor first run with a new boat.

We are not having a conversation about "nothing" several of the posters have helped me a lot and I thank them for that.

Boats&Outboards · 30 October 2011, 10:19

Provided the Mariner was fitted correctly then the MERC should just drop right in place, just make sure it's not sitting on the transonic itself as discussed

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

Dirk Diggler · 30 October 2011, 10:26

A 90hp on a 5.2metre rib, I'd being fitting it with the cav plate at least 1" above the bottom of the running surface.

Courageous · 30 October 2011, 10:30

Ok Burt, giving you the benefit of the doubt and that English is not your native language I say again in big letters "ASSUMING IT WAS SET UP PROPERLY ORIGINALLY". Granted you can't necessarily assume that. In any case a simple search would have led you straight to the answer to your issue here.

sburt10 · 30 October 2011, 10:41

Quote:

Originally Posted by Courageous

Ok Burt, giving you the benefit of the doubt and that English is not your native language I say again in big letters "ASSUMING IT WAS SET UP PROPERLY ORIGINALLY". Granted you can't necessarily assume that. In any case a simple search would have led you straight to the answer to your issue here.

Thank you for your 2nd rude and unhelpful post on a thread where I am simply asking for advice.

I am certain you know that English is my primary language. I presume marine engineering is not your occupation.

Having never seen which holes on which the outboard was set at and being that I do not have a time machine to go back and see what it was set at I thought I would ask a simple question on this forum. As I said, many of the replies have been very helpful, your comments have added nothing to this discussion.

Boats&Outboards · 30 October 2011, 10:43

Quote:

Originally Posted by sburt10

Thank you for your 2nd rude and unhelpful post on a thread where I am simply asking for advice.

I am certain you know that English is my primary language. I presume marine engineering is not your occupation.

Having never seen which holes on which the outboard was set at and being that I do not have a time machine to go back and see what it was set at I thought I would ask a simple question on this forum. As I said, many of the replies have been very helpful, your comments have added nothing to this discussion.

Nor mine to be fair

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

sburt10 · 30 October 2011, 10:46

Quote:

Originally Posted by Boats&Outboards

Nor mine to be fair

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

B&O, I am very thankful for your help, you are obviously very experienced in what you are talking about and you have been kind enough to share your knowledge with me and from what I have read on the forums, with anyone who needs assistance.