Changes to a factory-built boat - improvements, or mistakes?

[Greenheart]

A previous owner cut the rear cockpit bulkhead out of my Osprey dinghy. This may have seemed like a good idea for storage (and because Mk2 Ospreys have been criticised as floating very high at the stern when capsized) and because it allowed a roughly-cut transom-drain to shed water if the boat's really flying.

But the stiffness of the rear deck has been compromised by the change, and it's cracking badly under any weight.

I'm thinking I'll re-cover the space (it's about 34" x 16") with a sheet of stiff ply, bolted/Sikaflexed in place, and I'll seal the transom flaps - they're only taped on anyway.

As this GRP boat was one of many from a mould, is it fair to guess that the original design was better than my crudely-modified boat - or will I regret the restoration?

 

[prv]

Modifications to a boat can be improvements, if well-designed and executed, but often they fail at one or the other - or both! - and detract from the original. Yours sounds like it's in the latter category.

Pete

 

[Trundlebug]

Changes to any manufactured item can be satisfactorily carried out if properly planned, engineered and executed. (As prv said above)
Whether they are improvements or not depends on the quality of the original design, and whether the use has changed.

Many people think that because things look superficially possible, and they have some basic DIY skills, they can change the design.

Unless they also have some engineering skills, by which I mean an understanding of why things are the way they are in the first place, what function they serve, and the consequences of any changes they intend to carry out, things can go very wrong indeed.

An understanding of engineering principles, structures, forces, material properties, design, failure modes and numerous other factors that are cumulatively what real engineering is about, but are so widely misunderstood and undervalued particularly in the UK mean that there are an awful lot of bodgers out there who think they can do anything because they bought a tool kit from B&Q.

Scarily, sometimes they can go wrong many years afterwards when least expected, and often to different owners who didn't know anything had been changed.

 

[Greenheart]

Hmm. Well I hope my old boat is a recoverable example of ill-considered 'improvement', rather than a time-bomb of miscalculation and slipshod work!

It's not clear to me why the earlier owner expected such quantities of water to come aboard, that he'd want a massive transom drain as well as the self-bailers. Nor is it obvious why (having decided he wanted the rear compartment to flood) he didn't just plump for the small grooves sometimes seen in Mk2 Osprey decks to allow water in - because, by removing a whole bulkhead instead, he's really reduced its structural stiffness.

I'm hoping a 4mm ply replacement bulkhead will be rigid enough to help. Is it worth spending on a high grade of ply? It won't be submerged often, or for long periods (I hope!)

 

[Lakesailor]

Pictures!

If you want to restore integrity think about bonding it in rather than bolting. Use epoxy as that will bond better to the wood.

I have a feeling this will run and run

 

[lw395]

Self bailers only work once the boat is moving.
My current dinghy uses transom flaps to shift the bulk of the water.

I'm not that familiar with older Ospreys, but I suspect cutting a big hole in the aft bulkhead is not going to weaken the stern deck and cause cracking. If the deck flexes it will crack. It may not really be intended to be load bearing. The bulkhead only supports it along the front edge, is the cracking due to the middle of the panel flexing?
If there is a vertical bit forming an angle with the deck, that will likely make the front edge stiff enough? Maybe this bit is not big enough, or is itself cracked?

Excess buoyancy can make a capsized dinghy invert quickly instead of floating on its side, as well as making it harder to climb back in.

Personally, I would find someone with specific knowledge of Osprey variants and mods before doing any work on this.
Maybe a simple reinforcement of the front edge beam, or adding a simple post or something would be better?

Alternatively, if you do re-instate the bulkhead, some dinghies go for serious drain tubes through the rear tank which can work very well if you sit aft and bear off!

Some helpful and knowledgeable people when it comes to older dinghies on the Yots'n'yotting forum.

 

[Greenheart]

Alas I can't find the pics of that end of the boat...it's not exactly photogenic and I didn't take many.

It's likely the rear deck wasn't designed to carry much crew weight...but even my slender form, leaning briefly over the stern to reach the rudder, cracked the deck above the area where it's been cut away...and the crack is creeping. It's not a big deal - but I reckon it'll be stronger and better if I make it like the builder intended, once again.

I'll only be really miffed if I then discover some reason to wish that it was once more modified, as it is now!

Drain tubes sound like a good plan.

 

[William_H]

Just generally referring to modification of boats. Boat builders especially of production boats are always looking to cut costs. So yes you can modify and especially add to a boats gear to improve it. A boat builder has a wonderful advantage over us owners in that after building and sailing or selling a boat he can use the experience to improve on the next boat he builds. Such that after a few huindred examples we would hope many problems have been ironed out. On the other hand with cost restraints many boat builders keep onm producing the same old product when improvement could be very beneficial.
having come from the aircraft industry where it is ilegal to modify a plane I love to use my imagination to modify my boat. If i stuff it up well that is the price I pay for that freedom.
So I am often dismayed at how much trouble an ownwer on this forum seems to go to to keep a boat as built especially in rig when it wasn't a specilly good design in the first palce and changes could be far better. good luck olewill