Extending a Mk 1 from 50 to 55 ft

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Insequent

Insequent

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Mar 17, 2012
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Australia
Vessel Name
Insequent
Vessel Make
Ocean Alexander 50 Mk I
I have noticed that there have been a few Ocean Alexander 50 Mk I's extended. But I'm not sure whether many had engines etc relocated aft at the same time. Does anyone have any experience with these extensions? I'm curious about trim and sea-keeping behavior pre- and post-extension. I am contemplating it, but would like to get more comfort around what issues have arisen and how they were managed.

Insequent is currently getting a new foredeck. I'm guessing that the teak seams leaked a little, and with over 900 fasteners (passage into the balsa core....) it was inevitable that the core got soggy and rotten. I think the PO like to keep it sanded for many years, thickness of the teak was quite diminished in some areas.

Cheers - Brian
 
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I've managed to get a bit of information on costs but nothing really on trim/handling etc, and have got far enough to decide that this is not happening for me!

One yards estimate was $125,000 including full AwlGrip paint job. I keep hearing that gelcoat matching doesn't work as new/old fade differently, but no paint would mean it is a lot cheaper.

Another indicative pricing was "$15,000 a foot when we did the last one a few years ago, and resin prices have doubled since then. We would just use a couple of guys and take 4-5 months to do it." Easy to see six figures for that yard too.

These prices excluded shifting engines/props/rudders, and only simple tankage in the extension.

Seems to me that it just isn't worth the cost for an old boat. Instead I may DIY a 3 ft swim platform that bolts through the transom and extends the hull lines by that amount. No increase in cockpit area, but 60% of the waterline length increase so some benefit from that. My existing swim platform bolts on via brackets, but at 2 ft is a bit narrow, and the brackets might not have the strength to support a wider platform.
 
At those prices fabricating custom SS brackets and increasing the swim platform size would be my choice too. We've seen more than a few boats we wished had longer cockpits.

I have heard that most of the boats that have been extended never had running gear extended/relocated and was told handling suffered somewhat because of it.
 
Extending an OA Mk1 hull via boarding platform

I have a 1985 OA Flushdeck motor yacht; this was one of the last vessels built utilizing the Mk 1 hull (the deckhouse is different to the Mk 1 pilothouse design). I spent some time researching the various hull extensions that have been developed over the years to correct the too-small cockpit on an otherwise near-perfect design. Literally extending the hull (and without even considering re-locating engines & running gear, which would be plain crazy) is far too costly. However I did find a very happy compromise, which was to engage a naval architect to work with a skilled boatbuilder to create a boarding platform add-on with complete structural integrity. An image of the completed platform is attached. It creates a 2.5m extension including a big usable boarding platform and storage lockers. Half this width is literally a boarding platform suspended on glassed-in members above the water; the lattice deck copes with following-sea surges. The inner half of the extension IS a hull extension, fitted to the original hull and maintaining its below waterline lines but starting 300mm or so in from each side so we didn't even need to touch the exhausts. The interior of this inner half contains a ballast tank that I keep filled with fresh water, to offset the increased displacement of the additional hull volume. Because the 'real' below-the-waterline extension is only about 1.2m, there has been no impact on handling at all. Hull speed improved by around 0.75knts. Have been in very big seas with no issues. All works very well and didn't break the bank. I have during-construction images if any would like to see them: just PM me for them.
 

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Aquabelle,
That is a great extension. PM sent - I'd love more details.

I also like the stainless tube/teak extension to rear, and I assume sides. I'm contemplating that as well and it ties in with existing lines on the sides. Do you have photos? Have you extended the rails around the foredeck - that's an area that makes me nervous. The GRP at the bottom flares outwards, then the rails seem to extend that, with a result that I am going to ban people on the foredeck underway. With the Portuguese Bridge and seat there is still lots of scope for 'wind in the face' travel. An improved rail design on the foredeck is a better solution, although style and design will be critical for aesthetics.

Cheers - Brian
 
My OA Mk 1 has the Ed Monk designed 5' extension. Being new to the trawler world I'm not sure my experience allows me much credibility to comment on how it handles, especially since I have never operated a Mk 1 without the extension. My engines and rudders were NOT moved. Tight quarters maneuvering is excellent. I crossed the Strait of Juan de Fuca in about 4 foot seas and noticed no handling issues. I'm told if there are issues it will be in higher following seas but have not experienced those conditions yet in this boat.
 
Hi Randy
Glad to hear the handling is good without moving the underwater gear. I have wondered about what effects their might be.

I'm shipping back to Brisbane in about a month, and I'm still looking to do some kind of extension after I get back. It might end up as an enlarged swim platform that continues the lines of the hull. I would like some extra bouyancy at the stern. I enlarged my aft fuel tanks by 240 GL and when full I think the boat is a little low in the stern.
 
Aquabelle said:
I have a 1985 OA Flushdeck motor yacht; this was one of the last vessels built utilizing the Mk 1 hull (the deckhouse is different to the Mk 1 pilothouse design). I spent some time researching the various hull extensions that have been developed over the years to correct the too-small cockpit on an otherwise near-perfect design. Literally extending the hull (and without even considering re-locating engines & running gear, which would be plain crazy) is far too costly. However I did find a very happy compromise, which was to engage a naval architect to work with a skilled boatbuilder to create a boarding platform add-on with complete structural integrity. An image of the completed platform is attached. It creates a 2.5m extension including a big usable boarding platform and storage lockers. Half this width is literally a boarding platform suspended on glassed-in members above the water; the lattice deck copes with following-sea surges. The inner half of the extension IS a hull extension, fitted to the original hull and maintaining its below waterline lines but starting 300mm or so in from each side so we didn't even need to touch the exhausts. The interior of this inner half contains a ballast tank that I keep filled with fresh water, to offset the increased displacement of the additional hull volume. Because the 'real' below-the-waterline extension is only about 1.2m, there has been no impact on handling at all. Hull speed improved by around 0.75knts. Have been in very big seas with no issues. All works very well and didn't break the bank. I have during-construction images if any would like to see them: just PM me for them.
Click to expand...

I am interested in viewing the pictures of your transom extension. What a great improvement. I have a OA 50MK11 and getting on and off the boat is a chore. Not getting any younger. Looking forward to viewing your pictures.
 
To whet our appetite until/if Aquabelle shares those photo's...here's one way to do it;

Details
 
Basically extending a boats length is almost always a good idea.

But ... there are many variables. If the boat has a CG too far aft it will even fix a problem. But if the CG was too far fwd it will make a problem worse. Windage, slow speed maneuvering or high speed maneuvering issues can go south from an extension. The tendency for a boat to plunge her bow into a headsea will be changed. With short seas or far apart? Many variables.

A significant length addition to any boat is a very significant change and will have affects .. as in several to many.

But the biggest question is probably "would that change the CG for the better or worse?". The rudder authority question can probably be solved by increasing the rudder size. But like the CG the rudders may be too small or even too big in the first place. All these elements of design need to be known beforehand to be able to say if the extention is a good thing. Ideally it would solve a problem and create no others.
 
CPseudonym wrote in 2012,

"I have heard that most of the boats that have been extended never had running gear extended/relocated and was told handling suffered somewhat because of it.[/QUOTE]

One would think that would be a given ... if the boats design elements were optimum in the first place.
 
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Nomad Willy said:
One would think that would be a given ... if the boats design elements were optimum in the first place.
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One could replace/modify the existing rudder with a Schilling (fishtail rudder) and have equal or even better close quarter manoeuvrability.
 
Murray you may be right.

But on big stern seas w lots of water flow over the rudder that may not be so.
 
I believe Aquabelle was unwell recently but hopefully he has recovered and will post some pictures. I have some that he sent me a couple of years ago that I'll try and find if he has not responded within a little while.

Many of the OA Mk 1 hulls have been extended by 5'. Some were designed by Ed Monk Jnr, the original designer of the boat. So Aqubelle's 4' hull extension is not unusual although the additional length in the platform beyond that very likely is unusual. I am still contemplating doing the same, although I would go full hull width as dealing with an exhaust extension is not that much additional work or cost, and I think could give better performance.

I seem to recall a rule of thumb that a 10% hull extension on a boat can be accommodated without much issue at all, so 5' on a 50' boat would fit that 'rule'.
 
MurrayM said:
To whet our appetite until/if Aquabelle shares those photo's...here's one way to do it;

Details
Click to expand...
Thanks for the pictures they were very informative. Your project came out really nice. One question I have is how did you connect the stringers to the hull?. Any information I receive is really appreciated, Thank You.
 
Sunnydays said:
Thanks for the pictures they were very informative. Your project came out really nice. One question I have is how did you connect the stringers to the hull?. Any information I receive is really appreciated, Thank You.
Click to expand...

Sorry, but that's not our boat. I found it by typing into the Internet browsers search bar:

"hull extension" trawler

...then clicking:

images

...then looked through the photo's displayed and clicked on the ones that looked interesting.

Search engines (Google, Firefox, etc) are your friends :thumb:
 
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OA 50 mk1 flushdeck hull extension

Hi guys.
Considering that this post is fairly old, not sure what response this will get, but anyway.......
After much research, homework and anti social behaviour to the rest of my family, I bought is an OA 50 flush deck mk1 out of Southampton UK.
This boat has had a 6’ extension, giving it an amazing back deck area, but I think the previous owner lost his way when it came to finishing of the cockpit. So there’s plenty of work to be done there. Love a project.
However, all the running gear was left in the same locations along with engines etc.
He beefed up the size of the rudders and I think the shafts stayed the same 2”Dia.
He installed bow and stern thrusters, and also Trac Stabilzers.
The wet exhausts no longer go through to the stern, but exit the engine room in a very short vetus 6” hose from the new upright vetus mufflers that then hook up to the new 300hp JD’s he installed.
We came across Bay of Biscay when it was like a mill pond(such an anti climax) and further down of Portugal had some 6’ following seas that didn’t cause to much concern.
So how does she handle with a ton and half of concrete in the new centre rear hold?
So far so good, but as she’s now in France, I’m sure we’ll get plenty of chances to test her on our way to Aus.
 
Welcome aboard Almad!

You might like to start a new thread on your journey to Australia, it should be fascinating to follow along.

I never did get to do a hull extension. It is not completely ruled out, neither is it a priority. I've done about 2000 hours on the new engines after my refit, and assorted relatively minor repair and replacement projects during that time.

I still think the Mk1 hulls were very solidly built, and the Mk1 has a great layout in both the pilothouse and flushdeck variants.
 
2000 hrs. Looks like you actually get to enjoy your boat. Good to see your still going strong. What did you repower with?
I won’t bore you with to many questions except to ask where was your last cruise and where is your next one?
 
I repowered with John Deere 6068's, turbo but no aftercooler, which at M3 rating are 201 HP each. I normally cruise at 1600 rpm, so they have about 30-35% load each and I'm doing around 8 kn using about 20 litres per hour total.

Last year I did a 5 month cruise along the Great Barrier Reef. This year I've just been local around Moreton Bay as I am doing work on my house. Found termites downstairs so I've done a fair amount of demolition to uncover the damage. Now waiting on builders to complete the renovation, so I can get out on the Bay a bit more while I'm waiting. My twin daughters have moved out so when finished I'll likely sell it and 'do a seachange move'. It's all going to take time so no long cruises are on the horizon at this point.
 
Welcome aboard and congrats on your new boat.
 
Almad, you're motoring your boat from France to Australia?? Yes, you should definitely post a new thread. You can't leave us in suspense like that...... Lol
 
Hello Almad,
Our boat is a 1985 OA 50mk11 with the aft cabin, this makes our aft deck about 7 feet above the waterline, so boarding from the dive platform you have to climb straight up. That was the reason for the interest in the hull extension. Due to time (we wanted to use the boat) and budget constraints we put the project off for a while. Since launching we've put around a 1000 miles on cruising the Florida Key's and Biscayne Bay. Some of the issues that we have are lack of sightline when backing up into the slip. We find that good walkie-talkies are a must for docking. We're really enjoying the boat, though we haven't been in any seriously adverse conditions. Good luck with your voyage to Australia. We'll follow you on the forum.
 
Hello everyone. I just purchased an OA 50 Mk 1. I would like to extend her 3-5' and add in a swim grid that is just a continuation of the hull. Rather than the brackets bolted thru the transom. I have extended two of my commercial fish boats already. So I am comfortable doing it myself. I am also looking at passive stabilization as opposed to hydraulic. Back in the late 70's and into the 80's commercial boat builders were installing "Bat Wings". They were very effective but were in the way for longing and trap hauling fisheries. So most switched to rolling chocks or bilge keels.
 
I have not as yet done the extension I mooted way back when I started this thread. It would be nice to have. I would extend the boat deck above an extension to keep the dink there, freeing up a lot of space.

I love my Naiad's, I always have them on. Would not be without them. But I'll likely soon add some flopper stoppers for when at anchor.
 
greypearl said:
Hello everyone. I just purchased an OA 50 Mk 1. I would like to extend her 3-5' and add in a swim grid that is just a continuation of the hull. /QUOTE]


GreyPearl, I did exactly this with my 1985 OA Mk1 some 9 years ago now. Very, very happy with the result. The increased buoyancy created by the hull extension can be offset by building in a water tank as part of the swim platform.
Click to expand...
 
I feel like the prodigal son, but after a lot of miles under the keel, well, I’m back in Aus in isolation. But it was worth it!
First trip was with the ‘boys’ from Southampton to Gibraltar where the family joined.
Then up the East Coast of Spain to Ibiza and Mallorca and across to Barcelona.
Then did the sth of France, one we thought we could take or leave, but it was fantastic.
Got locked down in a big, like really big boat storage yard near marseille for three months because of covid.
Made the most of this time making friends, learning French-not, and of course a multitude of boat projects.
Once ‘released’, did sth france again, then down to Corsica and Sardinia. These were the pick, in a different way.
We were supposed to go down to Tunisia, but they went into lockdown, so went along Sicily and did the volcanic islands of there. You can clearly see one spitting at night!
From there we went bottom of Italy and up East Coast with the boat now in a lovely little fishing village of Vieste.
We had a lot of flights cancelled getting home due to Aus lockdown, but we had a great place to stay and was really safe.
Lake Como was beautiful, just couldn’t figure how to get the boat there��
What did I learn? Sailing on the ocean, free to roam, Breeze in your face, salt on your skin, rocking to sleep at night. All overrated.
Quarantine is where it’s at for me. Air conditioned. 10’ cubicle. Food that is mash. No maintenance work. Shrinking away to a mountain. Ahhhhhhhhhh
I’m sure you get the idea.
Our OA has got ABT Stabilzers that work a treat. But while in isolation, one of the projects was fabricating a Stabilzer I found on the world wide internetweb that you might have seen.
Found the materials in a local recycling yard and a bit of local talent added the rest. Only trouble is I haven’t worked out how to include a photo, so maybe that’s my project for today.
 
In the 70s and 80s, it was not uncommon to put a 6 foot extension on a 42 foot aft cabin motoryacht. Example: several Uniflite 42 ACMY were extended into a Uniflite 48 yacht fish. Running gear was rarely - if ever relocated. I had a client with a Cheoy Lee 65 that added a 7 foot extension. No change to running gear. He placed the generator in the aft lazerette for some reason I don't recall. He had other work done too, but took over a year.

Perhaps owners of defever 44 or 44+5 (a 44 with a 5 foot extension) could chime in with discussion of whether any material design changes except the obvious extension.

This is a job for a low labor cost location. But it will won't be cheap.

Peter
 
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