Outboard Height on F-rib

[mm289]

Hiya,

now I am getting out on the Frib a bit more I am starting to do some fine tuning so looking at the height of the OB on the transom. I know some of you Aerotec'ies have spent a fair bit of time working on this so thought you might have great input to make

Setup is F-rib 330 with a 15hp Mariner 2 stroke.

Goes really well, good for about 20kn when out on my own but particularly when 3 up kicks up a lot of spray from the leg so I though I would have a bit of an investigation.

Below is a pic of the boat at rest with 3 of us on board



As you can see the cavitation plate is well below the water line and when on the plane the boat seems to be dragging a lot of the leg through the water (no pics of that )

So I thought i would check how the engine was sitting on the transom and found a few potential issues that I would appreciate a bit of input on.

1. Because the transom is so thin you end up winding in the mounting bolts a long way. This is actually causing the cutout on the motor to foul on the transom lip and tilting the OB slightly



I have been running the OB in trim position 2 but playing with it out of the water if I try to get it to position 1 the leg hits the transom lip.

So I am thinking about putting a plate on the outside of the transom to create a thicker mounting point and straighten up the OB, something like this mock up.



Is this a sensible idea?

Apologies for the pics but every portrait pic seems to rotate to landscape on Rib.net and I can't find a way to fix it

Question 2 coming in a mo

Cheers

Paul.

[mm289]

Second and related question is can/how far can I raise the outboard.

At the moment on trim position 2 the cavitation plate sits about 1 1/2" below a line drawn from the centre of the V on the hull (top of the ruler in the photo)





If I fit the spacer plate described in the previous post and drop the OB onto trim position 1 this distance increase to about 2 1/4"




I mocked up a 1" packer on top of the transom but this starts to push the clamps to the very top of the mounting plate and raises the bracket too far I feel.





But it does have the effect of putting the cav plate only 1" below the hull on trim position 1 or 1/2" on trim position 2 (top of ruler is hull line)





So I am thinking the most I can go is to fit a fit a 1/2" spacer on top of the transom to raise the OB and at least get the cav plate closer to the surface/hull line.

Any thoughts on this or any other suggestions on trimming/adjusting the OB gratefully received.

Cheers,

Paul.

[beamishken]

The transom height is kinda weird seems like the transom must be 13" instead of 15" for your engine to be almost 2.5" too deep. Other possibility is the engine length, have you checked the distance from underside of saddle clamps to av plate?
Usually engines can run slightly higher than the bottom of the hull 2" below is way too deep.
The distance you can lift the engine without compromising the clamps will be pretty meaningless. It looks like the only way to get the engine high enough would be some form of extention plate which im not keen on. Maybe measure the engine and hull and report back to see where the variation is

[mm289]

Your wish is my command, he says trotting out to the workshop......


Back again...

- so transom height is 26cm/ 14" (although according to the owners manual it is 15"?)
- OB leg length measure from underside of saddle clamp (top of the u-bend) to AV plate is ~42cm/16.5"


Cheers,


Paul.

[Max...]

Search back for Locozodiacs excellent tutorial on mating engine to SIB, linked in the Which SIB sticky I think.

Engine height is discussed at length there. If transom is thin then adding a plate seems a good idea. Aerotec issue with splashing is due to unusual V of hull and the way it ends at the transom and directs water against the leg. Again pages of discussion on this and fixes (bodges!) with raiser shims, deflector plates etc.

[beamishken]

Originally Posted by mm289

Your wish is my command, he says trotting out to the workshop......


Back again...

- so transom height is 26cm/ 14" (although according to the owners manual it is 15"?)
- OB leg length measure from underside of saddle clamp (top of the u-bend) to AV plate is ~42cm/16.5"


Cheers,


Paul.

That explains the missing 2.5"! You could probably lift the engine by 3" and be a better off performance wise.
Some short shaft engines are a little longer than others which is what you have however that problem is being made worse by a boat made with a too short transom.
How you raise it is another problem. I have seen boats with a plate bolted inside & outside of the original transom with a 2 or 3" block the held above the transom either bolted or welded to the plates to clamp the engine too. It doesnt look prety but might help if you realy dont want to live with it

[Fenlander]

I assume the transom is thicker than the the yellow looking edge of the lip at the top? Anyway regardless of height I'd want a decent hardwood pad on the ouside thicker than that plastic pad it has already. OBs grip wood so much better than those flimsy plastic pads.

Re height see the image below. For over a decade I've aimed for the anti-ventilation plate immed above the prop to be in line with the lowest part of the hull and its worked well. For absolute maximum performance and minimal splash... I think as Beamishken is saying... you can have the AV plate an inch or so above the hull lowest point but in a SIB this often comes with the risk of losing prop grip in turns and some sea states when one up.

Ideally you would have a chunky hardwood rear pad made** that included the chosen raise and then an inner alloy plate made to the same dimension all bolted through to sandwich the existing transom.

**If it makes sense have a hardwood rear pad machined so in one piece it sat against the transom over the area where you take off the plastic pad... have a groove that allows the lip and then thickens out at the top so it's in line with the front face of the transom so the new larger inner pad (alloy) sits flat against it.

Personally I would just go with the AV plate level with hull bottom but if you wanted to see if higher was better it is better to go a little higher as you can always cut it down after water trials but don't want to be adding packers after going to the trouble of getting someone to make up the inner/outer pads.

I would also start bolting the OB to the transom... I do this now I have a broadly similar raised arrangement on the Aerotec.

[The Gurnard]

Hi mm289. If you sort the transom lip issue which is well know .. put a packing piece of 1/2inch under the outboard to lift it..still keeping its clamps withing the transom plate..I suspect the water getting thrown in the air will be sorted. At least it has sorted every other F Rib owner’s boat that I know..

Re the lip ... Many folks like myself and brother trim the excess lip flush with the outer edge of the plastic mounting plate. It removes around 1.5mm of the lip and is easy to cut with a dremel drill and cutting disk.. or a file and sandpaper. I ran a smear of epoxy glue along the cut edge to seal it and four years later its not shown any issues.

Some others have bought plastic cutting boards for use in kitchens ..cut them to the shape of the plastic motor mount ..unscrewed the motor mount and fitted the cutting board behind it before screwing back on. A very neat solution.

Both methods work well ..so choice is yours.

Transom is 22mm thick and has the strengthening top lip of 55mm wide ..so plenty strength. Not heard anyone having issues with it breaking and as far as Im aware the boats have been made that way for 5 years now.

Incidentally my transom height is 16” but mine is the smaller 2.75 size..so cant confirm the F Rib 360 transom height.

However Reading your description.. there is something not adding up when you say that .. when OB is on pin 2 pin one the AV plate is half an inch below transom ..and you also say the transom is 14” and outboard from AV plate is 16.5” ..if my maths s correct 16.5” minus 14” = 2.5” so how can it be half an inch below transom on pin 2 ?

Edit after reread ……. Sorry I now notice you have 1" packing piece in..so put half inch packing piece and you will be at 1" below transom..which is what most the F Rib guys have.AFAIK

. You also say the transom height is 26cm/14” when in fact 26cm is just over 10 inches. Possibly typos ..but worth checking.

I know many F Rib owners and they all had the Lip issues and some had water thrown up in the air behind the boat depending on OB brand ..the half inch packing piece solved the water issue. Yes..the AV plate will be running ½ to 1 inch below the transom.. but getting 25knots one up in a small lightweight boat with a 15HP..which is my brothers best speed..is good going regardless how far below or above the transom it is.

Hope that helps..

[mm289]

@max thanks for the link - I have now read Locozodiacs post and that makes sense


@Beamishken - yep, not quite an ideal match


@Fenlander @gurnard - all makes sense and kinda aligns with what I was thinking. Thanks for taking the time to put a detailed response.


I will look to make up a plate for the outside of the transom - probably from marine ply suitably treated. Whilst experimenting I will probably Sikaflex it to the plastic plate as I have had good experiences of that holding the transducer mount on and avoids drilling holes etc until I am happy with the setup.


Re the lift - thanks @gurnard for the expereinces from other Frib'ers. I wasn't keen on too big a lift as it takes the OB mounting clamps really high on the transom and the only way I could make that work is to make up a "transom extender plate" which I think is pretty much what fenlander is describing.


So will probably go with the 1/2" lift to start with and see what difference that makes.


The real driver for playing with it is the amount of spray it creates as it drags the leg through the water - not so much of an issue when I am 1 up but when 3 up it is quite noticeable. Also I think the noise it is creating may be causing havoc with the transducer........


So off to the wood workshop to play with some hardwood and ply


Cheers,


Paul.

[jeffstevens763@g]

my engine was 50 mm low because of the transom angle so i fitted a 40 mm HDPE block.

[Fenlander]

I think Donny's real life advice is a good starter and likely actually the final solution. With the Aerotec the ideal raise for most OBs needs a bit of construction work such as in the image below but most folks just go with the largest packer (20-25mm) that keeps the outboard clamps on the transom and that works near enough..... which is what I did for a few years.

In truth 90% of the result for 10% of the effort is always rewarding!

[The Gurnard]

A wee tip for anyone who needs a packing piece to lift the OB …

While I appreciate many folks are happy to sit it on top of the transom ..or even screw it on so they don't forget it.

I prefer attaching the packing inside the OB clamps and held in position with cable ties. The picture shows my F Ribs half inch packing.. its a fit and forget solution :-D

Of course it has to be small thickness packing so the clamps still fit in the transom mount plate. If raising further you need will need to do something like Fenlander did

[mm289]

Thanks all - and that's an ingenious idea Donny


I need to sort it out as (lockdown permitting) we are staying on Loch Striven for a couple of weeks end of July and I want to bring the Frib to spend a day or two on Loch Striven around to Kyles of Bute


Cheers,


Paul.

[The Gurnard]

Originally Posted by mm289

I need to sort it out as (lockdown permitting) we are staying on Loch Striven for a couple of weeks end of July and I want to bring the Frib to spend a day or two on Loch Striven around to Kyles of Bute
.

I hope you can mm289 but after today entering phase 2 in Scotland, I would not count of coming to Scotland for holidays this year.

Only an hour or so ago our leader has ”Sent us all homeward to think again” and again not allowed us to travel further than 5 miles to go boating fishing etc. She said she would lift the restriction of travel for us on 15th July when tourist season may start.

Her reason given is she wants our R number and cases as low as politically possible. Why she would do that then let tourists in from areas with high R numbers in July does not make sence ..unless she plans on making the tourist season in Scotland for Scots alone.. which would not surprise me.. after all is it not why Scotland and Wales are not allowing folks to travel far across borders at present.?

IMO..its no longer about pandemics..its about politics and Nippy is making the most of her Independent Scotland

Whatever happened to the Scottish Freedom speech.. “You can take our lives.. but you will never take our freedom !!”

I never though the Scots were feart folks..but looks like I was wrong. Can I come to England for a holiday in July ? ..Im clean..honest.

[beamishken]

Originally Posted by The Gurnard

I hope you can mm289 but after today entering phase 2 in Scotland, I would not count of coming to Scotland for holidays this year.

Only an hour or so ago our leader has ”Sent us all homeward to think again” and again not allowed us to travel further than 5 miles to go boating fishing etc. She said she would lift the restriction of travel for us on 15th July when tourist season may start.

Her reason given is she wants our R number and cases as low as politically possible. Why she would do that then let tourists in from areas with high R numbers in July does not make sence ..unless she plans on making the tourist season in Scotland for Scots alone.. which would not surprise me.. after all is it not why Scotland and Wales are not allowing folks to travel far across borders at present.?

IMO..its no longer about pandemics..its about politics and Nippy is making the most of her Independent Scotland

Whatever happened to the Scottish Freedom speech.. “You can take our lives.. but you will never take our freedom !!”

I never though the Scots were feart folks..but looks like I was wrong. Can I come to England for a holiday in July ? ..Im clean..honest.

Well said!

[mm289]

@gurnard Oh gosh that's a bit grim


Doesn't help the tourist industry at all as all the cottages etc have started taking bookings and I suspect a lot of people (like me) will now be thinking ooooh, is this going to happen.


Even places like the caravan club and camping club were talking of opening sites in bonnie Scotland on the 15th so she may have caused a mild panic


Of course your always welcome down here but you would have to contravene the 5 mile rule just to get to the border and I cannot absolutely guarantee as nice cruising grounds to explore


Cheers



Paul (ever hopeful)

[beamishken]

Originally Posted by mm289

@gurnard Oh gosh that's a bit grim


Doesn't help the tourist industry at all as all the cottages etc have started taking bookings and I suspect a lot of people (like me) will now be thinking ooooh, is this going to happen.


Even places like the caravan club and camping club were talking of opening sites in bonnie Scotland on the 15th so she may have caused a mild panic


Of course your always welcome down here but you would have to contravene the 5 mile rule just to get to the border [emoji38] and I cannot absolutely guarantee as nice cruising grounds to explore


Cheers



Paul (ever hopeful)

If the places are open the 5 miles is a suggestion not a rule, It wouldnt stop me crossing the border.

[mm289]

Sorry, no update on the engine height but just been confirmed Scottish tourism is open for business from the 15th so looks like my trip up there is still on


Now to plan a few days out on the F-rib


Cheers,


Paul.

[Locozodiac]

Originally Posted by Max...

Search back for Locozodiacs excellent tutorial on mating engine to SIB, linked in the Which SIB sticky I think.

Hola Max,

Have finished writing a new Motor Installation Tutorial Review on the subject, way superior than the previous one you have mentioned. It's easy to follow, understand with many illustrations to avoid, be aware of and follow to the letter if possible for neat motor installations on any boat's transom.

Will send a copy tomarrow to John the Forum Moderator to have a look and evaluate, if gets the green light, will like to post as written to avoid posting photos separately from the text to follow and understand more easily...

Happy Boating

[mm289]

That would be great @locozodiac

So made some progress yesterday. I had a piece of Polycarbonate knocking around in the workshop so cut this to shape, sanded down the edges and have stuck on with Sika 291i.

Have gone down the Sikaflex route as this is just to locate the plate not load bearing, and I might end up replacing with a piece of HDPE like ?Jeff linked to in the other thread.





Then made up a block to raise the engine from a piece of oak. Profiled slightly to sit square between mounting plate and transom top.

This will get varnished then probably attached to the OB like @Gurnard suggested as the block won't work with the 6HP - see next post





With all of this done the AV plate still sits well below the hull by 2" but there is nothing else I can do know other than rebuild the transom which isn't happening




Cheers,


Paul