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Old 05-19-2012, 01:55 AM   #1
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Extending a Mk 1 from 50 to 55 ft

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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Old 06-01-2012, 07:09 PM   #2
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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.
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Old 06-01-2012, 08:59 PM   #3
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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.
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Old 06-15-2012, 08:15 PM   #4
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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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Old 06-15-2012, 09:45 PM   #5
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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
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Old 07-30-2013, 04:23 AM   #6
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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.
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Old 07-30-2013, 04:13 PM   #7
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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.
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Old 10-02-2016, 10:59 AM   #8
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Quote:
Originally Posted by Aquabelle View Post
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.
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.
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Old 10-02-2016, 12:31 PM   #9
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To whet our appetite until/if Aquabelle shares those photo's...here's one way to do it;

Details
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Old 10-02-2016, 12:32 PM   #10
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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.
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Old 10-02-2016, 12:42 PM   #11
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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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Old 10-02-2016, 12:51 PM   #12
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One would think that would be a given ... if the boats design elements were optimum in the first place.
One could replace/modify the existing rudder with a Schilling (fishtail rudder) and have equal or even better close quarter manoeuvrability.
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Old 10-02-2016, 02:28 PM   #13
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Murray you may be right.

But on big stern seas w lots of water flow over the rudder that may not be so.
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Old 10-02-2016, 06:03 PM   #14
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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'.
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Old 10-03-2016, 07:10 AM   #15
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I'm away from my home computer right now but will post photos here and respond to the various PM's as soon as I get back.
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Old 10-06-2016, 08:27 AM   #16
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Originally Posted by MurrayM View Post
To whet our appetite until/if Aquabelle shares those photo's...here's one way to do it;

Details
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.
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Old 10-06-2016, 09:26 AM   #17
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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.
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
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