What is the name of the bar that goes through the foredeck and attaches to the mast? (its controls are housed on the forward buoyancy tank and the lines feed to central cockpit.)
 
I have broken mine and not sure what its called.
 
Thanks for any help you may provide.

A Strut?

Surely a mast ram.  I assume that your mast is hog stepped and not deck stepped.

 Hi, I believe the mast to be deck stepped. However I am not sure about the hog stepped version. The mast disconnects at the deck, however below is a very short version of the mast which goes to the hull, this does not come out I guess this is just for support.
 

 I have added a you tube video/photo the the boat. You can see the bar I am talking about at the front end, its at 45 degress.
 
hope the video works and thanks for your replies, any help is precious!
 
 

 https://youtu.be/P7V7ICqwGFA 
 
I cant seem to work out the video thing but above is the link.
 
 

If it's a deck stepped mast, then this will be a strut. This should be quite easy to source a replacement for if repair is un-economic. (they are still in use on other dinghies today).

Hi. It's not the strut that's broken . Unfortunately it's the wooden housing below the deck above the buoyancy tank. It blew out on a gybe! About 25 knots!  

Has anyone had this problem before? 

Hi Neil. I'm assuming that the post and the previous one is leading to a repair of the broken part.  
If you let the forum know where you are someone might be able to suggest a repairer nearby who has worked on merlins before.  
I think the struts usually pivot around deck level in a cradle of some sort but there are probably many different ways of making that happen so without pictures of the parts that have broken, its difficult to say if an off the shelf spare is going to be possible.
Alternatively you might just want to glue the bits that have fallen off back on with some epoxy and see how it goes. Things often give up on older boats, sometimes its the older glues used, sometimes its just a lifetime of racing but in either case a repair is usually possible.  Just need to get it in front of the right person. Hope that is of some help!

 Thanks KM, its a relief to hear i may just be able to epoxy.  im based in chichester harbour and sail out of bosham independantly. (i use there quay for a small fee)
 
 
I really love the dinghy, such a  great boat to sail : ) she is a bit vintage now though but sails great! Hopefully i can fix her up sharpish before we loose this great late summer :) lol
 
Thanks again Neil

Neil - I'm sure it would be a help to those trying to help you if you gave the number of your boat, as construction techniques evolve over time.

I think Neil mentioned it was a 1979 Winderbox, 3161 in a previous post, some pictures under the foredeck and the mechanism used to adjust the strut might help?

 Hi,
 
If it is 3161 then it may be worth giving David Winder a call, as both he and his dad sailed this regularly (given that his Guy built it) in the 1990's and I don't think that much has changed since.  Dave would probably be able to point you in the direction of someone who could help.
 
I know that the Kingpost (the part under the mast step) was a M7 mast part, with a strut on the foredeck to regulate mast bend that was pivoted at that point.

 Hi here are a couple of photos of the housing.
 
  https://youtu.be/FhOlNTvUY-w
 
I will give the Winder people a call/email and find out about it aswell. 
 
Many thanks.

Looks like it needs epoxy both under the foredeck and on the top of the tank, but get a professional opinion on the rest of the structure as well.

 Thanks Stuart. Yes I think some epoxy also, I really need to strengthen the unit there for sure so i might add some extra's.
 
 
Profesional opinion good idea, will get that sorted! thanks.

 After my initial panic of having some broken parts, I have started work on 3161. I will say that accessing the fwd buoyancy tank and under the deck is mighty uncomfortable! especially working with a heat gun and scraper removing varnish. 
 Anyway I have a plan and its going to work : ) includes doubling up the marine ply on the piece where the whole is and basically strengthening the area that houses the mast strut. including epoxy and micro balloon fillets where ply meets ply. i guess this is standard stuff.
 
I did not want to take the deck off or change the ply on the tank, just way too much work for a job that can be sorted with a bit of tinkering here and there.
 
Feeling better now : ) sailing again this season for sure (light winds first tho!)