Transom Plate

[Duckfish]

Hi Guys,
Am planning to renew my donk but my transom is 20" so I was wondering what thickness stainless steel plate would I use to put across my transom to lift the new motor to 25"? I am planning to bolt the new plate across my transom and mount the new donk on to the plate. Any help would be appreciated. Thanks.
Duckfish

[Jarrah Jack]

What sort of boat have you got DF. With glass its not necessarily that easy as a 25 inch leg can put extra stresses on the transom in places where it has not been designed for.

Mustang5 went through the process and a marine surveyor recommended extra knees to handle the stress.

[finga]

Yep, size and type and weight of engine combined with particular boat are needed for an answer.
Anything above a 15hp and you'll probably need advise that's out of the knowledge boundaries of us here.

[Mr__Bean]

Anything above a 15hp and you'll probably need advise that's out of the knowledge boundaries of us here.

Most intelligent post I have read on here in a long time.

Darren

[BM]

Duckfish,

What you are wanting to do is not uncommon. I have done quite a few as have others.

Assuming you are not going outside the weight or hp boundaries of your transom then its a pretty simple approach.

The plate need not be as wide as the splashwell as it will serve no extra purpose and just look ugly. I make the plate about 30mm wider on each side than the transom brcket/clamp bracket. I also make it about 30mm shorter than the measurement from the bottom of the clamp bracket to the upper inside edge that sometimes sits on the transom top and sometimes doesn't.

The bottom bolts go through the engine, the plate and the transom. The next two bolts go OUTSIDE the clamp bracket but through the plate and the transom as high up as you can go. This is why the extra 30mm wide on each side, to accomodate the bolts with a 1 inch washer. The top engine bolts the go through only the plate.

If your engine is a V6 then 25mm plate is the sixe to use. A V4 and you could come down in size to perhaps 20mm (or stick with 25mm). Under 115hp I would suggest 20mm. BUt it would depend on engine weight etc.

From memory a plate would usually be about 360mm wide and about 450mm long (those figures ring a bell but it's been a while). Doesn't matter anyway as you will measure what you need. a palte of similar dimensions will usually cost you about $140.

Cheers

[FishHunter]

Seems pretty obvious to me that if you are buying a new motor just buy one with a 20 inch leg.

[dnej]

Fish hunter, getting a longer leg motor, gets it higher out of the water.
David

[Duckfish]

Hi BM,
You are on the money. I have a Haines 565L with a Mercury 175hp EFI which is a 1994 vintage and getting long in the tooth therefore a motor change is soon coming. I still need to know the thickness of the plate required but the other dimensions are very helpful. I have heard that Mercury has a 150hp Fourstroke that weighs 206kg but I am going to wait for 175hp hoping that it should weigh the same.
Hi Fish Hunter,
Dnej is on the money. With a 25" leg. the motor is higher above the water.

[finga]

Is the boat insured?
If so, then the first port of call would be to them to ask if it is OK to do.
And then I'd be buying something that is certified like these suckers http://www.cmcsales.com.au/pages/setback.htm. (http://www.cmcsales.com.au/pages/setback.htm) and http://www.solas.com.au/cms/index.php/Jacking-Plates/View-all-products.html
There's plenty of them around to buy off. Just Google outboard jacking plate

[BM]

Hi BM,
You are on the money. I have a Haines 565L with a Mercury 175hp EFI which is a 1994 vintage and getting long in the tooth therefore a motor change is soon coming. I still need to know the thickness of the plate required but the other dimensions are very helpful. I have heard that Mercury has a 150hp Fourstroke that weighs 206kg but I am going to wait for 175hp hoping that it should weigh the same.
Hi Fish Hunter,
Dnej is on the money. With a 25" leg. the motor is higher above the water.

Hi mate, I did mention plate size. 25mm

Cheers

[Fed]

I think you'll wreck a good boat jacking a 25" on it Duckfish, just my opinion.

[mustang5]

You just have to be careful with how wide you put the top bolt plate. Reason being, if you make the transom too stiff over the span of the splashwell, it will reduce flex. Flex is important as it dissipates the load evenly so if you apply a plate to the width of the splashwell, the loads will be directed straight to the sides and you will get vertical cracking in the glass leading to repair or worse..

I used a 10mm plate, which I had to rattle gun the top bolts for the plate to bend to the shape of the transom..

However, weight was more of an issue for me rather than the leg length. I had a 20" transom with a 25" 200hp yamaha without a plate, and did not have a drama. The only reason I went for a plate and knee braces was from going to a 207kg motor to a 269kg four stroke.

Food for thought anyways. Good fun hey :)

[odes20]

I put a 25 inch Suzy four stroke on my Yalta ODESSA which was only a 20 inch transom. My transom was soft as well so I completely rebuilt the transom including raising the height to 25 inch. The biggest problem you need to face is if the transom has any age about it, the chances of it having some soft patches or loss of structural strength will be pretty high. Trying a lifting plate on that will only create real problems. I would be really careful in assessing the transoms integrity, before spending money on the plate idea.

John

[finga]

How much would a 450 x 360mm plate of stainless 25mm thick weigh?
33-35kgs plus??

Weight would have to be a consideration too wouldn't it? Especially if your hoping the 175 weighs the same as a 150. What's the specs (ie max. transom weight) for the 565? About the 200kg mark?? And the motor you are wanting to fit is 206kg?

[Chimo]

Wouldn't you use Aluminium in preference to SS?

[Duckfish]

Hi Guys,
Thanks for your inputs. Hi BM. 25mm plate is pretty thick but I guess you dont want any problems. The reason why I wanted SS was to keep thickness down but BM reckons that the plate I need is 25mm so I might think about an aluminium plate. Going to a 25" inch leg shouldn't affect the ride or handling of the boat. I will mount the new motor at the same height as my current motor keeping the cav palte about an inch higher then the bottom the boat. My boat was built in 1981, long before compliance plates were required and the current plate only says that maximum hp is 175 so if I keep the weight down to about 210kg, it shouldn't pose a problem. I hope. I had thought about replacing the transom but the cost involved in doing so turned me off. I think the transom is sound because all my skin-fittings are all where they should be and not mis-shapen or moving. I had a Cruisecraft 550 Outsider and had transom problems. With the Cruise Craft the skin fittings were moving,ie the end fitting was moving to the end of the skin fitting, not the Haines. Thanks for your help guys.
Duck

[BM]

Hi Guys,
Thanks for your inputs. Hi BM. 25mm plate is pretty thick but I guess you dont want any problems. The reason why I wanted SS was to keep thickness down but BM reckons that the plate I need is 25mm so I might think about an aluminium plate. Going to a 25" inch leg shouldn't affect the ride or handling of the boat. I will mount the new motor at the same height as my current motor keeping the cav palte about an inch higher then the bottom the boat. My boat was built in 1981, long before compliance plates were required and the current plate only says that maximum hp is 175 so if I keep the weight down to about 210kg, it shouldn't pose a problem. I hope. I had thought about replacing the transom but the cost involved in doing so turned me off. I think the transom is sound because all my skin-fittings are all where they should be and not mis-shapen or moving. I had a Cruisecraft 550 Outsider and had transom problems. With the Cruise Craft the skin fittings were moving,ie the end fitting was moving to the end of the skin fitting, not the Haines. Thanks for your help guys.
Duck

I've never used a stainless plate but you could. I don't know why you would though. A mate of mine has been installing alloy jack plates for over 20 yrs also with no failures. I've done it for 8 yrs or so.

Stainless you would get away with a thinner plate but there's no point to the extra expense. You don't gain anything from it.

Alloy works exceptionally well and looks good and is practical. I would be surprised if your insurance company has a problem with it (check though obviously)

Cheers

[Duckfish]

Hi Guys,
Thanks for responding to my post. BM Sorry I didn't see your reply about the thickness of the SS plate. 25mm is a little bit thicker then what I wanted so an alumimium plate may be the answer.If I wanted the plate in alloy what thickness would you recommend? The boat was built in 1981 long before compliance plates were thought of but the current plate has stamped max hp 175 so I guess that a new 175hp Fourstroke maybe the go, weight permitting. I think that the transom is ok. The two skin fittings that allow water out of the splashwell are nice and tight. Usually if you have movement in the transom. the skin fittings will also show signs of movement. I had a Cruise Craft 550 Outsider with a dodogy transom and the skin fitting showed some signs of movement. Anyway I hope the transom is ok, time will tell.
Duck

[Duckfish]

Sorry. Double post.

[BM]

PM replied mate.

[odes20]

Just another query from me?
Doesnt such an arrangement look makeshift and dodgy? I thought about doing the same but couldnt bring myself to the messy look of the thing.

[Duckfish]

Hi Odes,
You are right that it will look unsightly but evryone will know what I have done so that's ok with me. A transom replacement is the go but I figure the cost involved would make it uneconomial. Now if I was to win Goldlotto this weekend, that would be different. Wish, wish.
Duck

[wayno60]

73640736417364273643

I know mine is only a small HP motor on a tinnie and could get away with it , but its just not the weight but the thrust of the motor that could do the damage...

[BM]

Just another query from me?
Doesnt such an arrangement look makeshift and dodgy? I thought about doing the same but couldnt bring myself to the messy look of the thing.

Nope, definitely not. That's why it's only made slightly wider than the outboard mounting bracket. It very clearly then looks precisely as a jacking plate should look.

Done it with expensive boats with expensive motors and the result looks natural and also looks good. I suppose you could even paint the plate white if you wanted to (assuming your board white) to make it blend in further but they look fitting to begin with.

Duckfish, you said 'transom replacement is the go' but I strongly disagree. After you fit a plate of appropriate dimensions you will see what I mean. They look 'right' and that's important.

Cheers