Lowering transoms

[Argyll Fisher]

Hi, just back from my local angling club committee meeting where a debate took place about whether 15ft open glass fibre fishing boats could have the transom lowered to accommodate a short shaft outboard. I realise that more detail would be required but in general is this something that maybe able to be done without compromising the boat structure and broadly what work costs etc would it involve? TIA

 

[Minerva]

Going by the adverts on Facebook, L/shaft o/b's are less in demand and command weaker prices than their S/shaft counterparts. So I'd have to ask - why bother?

 

[penfold]

Do the boats have outboard wells? What conditions are the boats being used in? Open sea? A lake? etc. Generally boats that size won't have a lot of spare freeboard and reducing it by taking a saw to the transom isn't a great idea. Swapping the shortshaft O/B for a longshaft is a better bet without knowing anything else.

 

[Argyll Fisher]

Thanks for replying. There are a number of members in our club with s/s o/b ‘s who are not inclined to change their o/b’s! The boats are used on large inland waters that can get rough! Maybe these members need to consider selling the s/s o/b’s and getting l/s o/b’s. Some of our boats have outboard wells and my feelings were that we should not lower transom’s on existing boats For fear of affecting the integrity of the boats.
is there any other options ? Can you fit an additional transom board that sits lower? Again TIA

 

[penfold]

That's pretty much it; if a boat has a well then lowering the transom is more an exercise in making sure to not weaken the structure, but if there isn't a well it's reducing the seaworthiness by a significant degree. If the outboard is an older one and they're emotionally attached to it, it may be worth posting a wanted ad for a deceased longshaft and transfer the powerhead, as it's more often the powerhead that expires than the gearbox.

 

[William_H]

Small sail boats often have a mount for an o/b external to the transom . Seems like a simple solution to me to mount a bracket on transom. There is sometimes a problem where pitching in waves lifts the o/b out of the water but I think with mobo with flat bottom at the back pitching not so much of a problem.https://www.whitworths.com.au/o-b-bkt-ss-25hp-58kg ol'will

 

[Thistle]

My immediate reaction would be similar to yours. Why has the boat's designer made the transom the way it is? Why didn't they design a lowered transom? If, like me, you decide the answer is "to retain freeboard and keep the water out", you'll leave the boat as it is.

As others have suggested, is fitting a lower mount aft of the transom a possibility? It may have to be offset to one side to allow engines to be mounted centrally direct on the transom and the effect that this may have on handling characteristics may outweigh any benefits obtained.

 

[Neeves]

You could extend the transom aft by 'simply' adding a shoe, call it a shelf. You maintain or follow the under water form, so from below you would not detect the extension. If you follow this idea then the addition is sealed and hollow - you can make it as high or low as you want and build in the reinforcing to take the outboard. It would simply be like a fancy swim platform.

It would be much easier to simply add a bracket that takes an O/B.

Jonathan

 

[wallacebob]

Outboard brackets that tilt or slide and are adjustable are commonly and easily available. Mounting at appropriate height is essential. Trem Stainless Steel Outboard Motor Bracket 15hp Gael Force Marine

 

[Bilgediver]

Hi, just back from my local angling club committee meeting where a debate took place about whether 15ft open glass fibre fishing boats could have the transom lowered to accommodate a short shaft outboard. I realise that more detail would be required but in general is this something that maybe able to be done without compromising the boat structure and broadly what work costs etc would it involve? TIA

This question is difficult to answer without knowing the design of the boat involved. The shaped gunnell at the top of the transom on some boats provides added stiffness to the structure and cutting into this without adding extra stiffness could lead to problems. if the transom is relatively high then cutting out a notch to take a short shaft motor may lead to problems of flooding in following seas hence the suggestion of fitting an outboard bracket is a good alternative.

 

[QBhoy]

I honestly am if the opinion that boats are designed and made the way they are for a reason…also think that should lovely wee boats like this be cut at or butchered, it’s not only a shame to see, but also likely to become an issue when the time comes to sell them on, should the boat be replaced for new, further down the line.
only other thing that may be a compromise, is to fit them with an auxiliary outboard bracket. You would get a short shaft on then. But not cosmetically pleasing or perhaps even too efficient, in comparison to the conventional. Also involved drilling a few holes too.

 

[ylop]

if it was your own boat, being used only in circumstances you control and where you know the user fully understands the impact of reduced freeboard, you can inspect the change for damage etc - then it’s probably not the end of the world. For a club boat it just seems like a load of hassle for no real benefit.

 

[boomerangben]

Are the boats owned by the club? If so what would the insurance position be? Would the insurers allow it? How would the club handle any incident arising from a chopped transom? I don’t like bringing these sort of things up in a leisure context but I think it needs to be considered. Hulls are designed to keep water out. Longshaft o/b’s are designed to be used on boats with too much freeboard for a s/s. Either the club bought the wrong boats or the members bought the wrong o/b

 

[Minerva]

Thanks for replying. There are a number of members in our club with s/s o/b ‘s who are not inclined to change their o/b’s! The boats are used on large inland waters that can get rough! Maybe these members need to consider selling the s/s o/b’s and getting l/s o/b’s. Some of our boats have outboard wells and my feelings were that we should not lower transom’s on existing boats For fear of affecting the integrity of the boats.
is there any other options ? Can you fit an additional transom board that sits lower? Again TIA

Fundamentally, changing club assets to accommodate club members own property feels a fools errand imo.

 

[Argyll Fisher]

Many thanks for all the advice, opinions and considers, very much appreciated. Personally I agree with the sentiments expressed re not altering boats and accessing the correct o/b for a particular boat. Unfortunately as I am finding out on a frequent basis, you can’t please all the people all of the time and consensus is hard to find!

 

[Boathook]

Let someone else on the committee sort it out and if they do decide to lower / modify the transoms, get it in the minutes that you object and won't take any responsibility for any incident that may happen due to the modifications

 

[Argyll Fisher]

Many thanks for all the information and advice provided. I am happy to report that we are not going down the original route of cutting transoms (not with my agreement at least) and are looking at purchasing an auxiliary outboard attachment.

 

[DownWest]

Doing a 'proper' job on lowering the transom would likely need a 'box/well' to bring the freeboard up inside the the transom. Prob way cheaper to get the long shaft kit to to extend the treasured motor.

 

[MisterBaxter]

If I were given the job of fitting a short shaft outboard onto a too-high transom I think I'd fit a stout horizontal plank mounted on two blocks onto the transom, just wide enough to take the outboard with the blocks just big enough to give the right clearance. Through-bolt right through plank, blocks and transom, glue on all joining parts. Oak or similar would work well.

 

[William_H]

If I were given the job of fitting a short shaft outboard onto a too-high transom I think I'd fit a stout horizontal plank mounted on two blocks onto the transom, just wide enough to take the outboard with the blocks just big enough to give the right clearance. Through-bolt right through plank, blocks and transom, glue on all joining parts. Oak or similar would work well.

Yes most expensive outboard mount brackets are designed for sail boat with ability to raise the motor out of the water completely. You only want a fixed bracket. You could fabricate one from a block of wood (for the motor to clamp on to.) 2 bits of angle iron (ali or ss) bolted to the outside edges of the wood. 2 bits of angle iron (ali or ss) to bolt to the transom. 4 pieces of flat iron (ali or SS) joining the angle bits at a suitable spacing top and bottom each side, then 2 more bits flat iron to triangulate to hold it up square. All bolted together. ol'will