Snapped my rudder!! Trojan 750

[danielfarley 0]

Hi,

 

My rudder went ping, see pic! and now i need a new one (was in Taupo and a few hours from port.. was a little fun getting back on the the aux ! ) ... Thinking of making up one my self but wondering if there is anyone who recommends a outfit to make one for me???

 

 

I think that if i do make one i plan to build a large jig to hotwire cut a foam to form a naca0012 foil for it, cut it out of some kind of high density foam... corecell is what i have been looking out although need to buy a whole sheet!! and is not cheep.

 

then glass and vacuum bag over the top of it

 

Any recommendations on other foam, to use? Anyone in the Lower north island who is trying to do the same / has set up too??

 

If i do make a jig i may make a proper job of it and make it to do other foil shapes as well and start offering blanks / finished rudders for sail. So is this something people would be interested in?

 

 

Thanks for any advice comments on this problem

 

Bring on the summer

 

Daniel

[Deep Purple 512]

Does the centrecase in the Trojan still fit flush with the mast bulkhead? The Trojan was adapted from the Stratus 747 plans and there was an error in them as regards the centre of effort. You can see it clearly on the Stratus 747 plans. The Stratus 747 centreboard version had the CLR well ahead of the CE. The keel version which I built had the CLR about a foot further aft. In a way it was a good safety feature common in many trailer yachts that had them round up long before they tipped over.

 

What this means to you is the Trojan rudder is going to have to be really strong especially if you have a lot of blade forward of the pivot point. Get professional help in specing a new blade.

[danielfarley 0]

Hmm.. Not sure been 6 months of being to busy to even start on the rudder... So havn't seen the boat in that time.. Going to be working part time soon, so will start having some time to fix her up and to use he too

 

 

Does the centrecase in the Trojan still fit flush with the mast bulkhead? The Trojan was adapted from the Stratus 747 plans and there was an error in them as regards the centre of effort. You can see it clearly on the Stratus 747 plans. The Stratus 747 centreboard version had the CLR well ahead of the CE. The keel version which I built had the CLR about a foot further aft. In a way it was a good safety feature common in many trailer yachts that had them round up long before they tipped over.

 

What this means to you is the Trojan rudder is going to have to be really strong especially if you have a lot of blade forward of the pivot point. Get professional help in specing a new blade.

[Kiteroa 8]

My mate used some of the rudder mould I have for WT on his 747, so that could work for you. Also, if you vacuum on to low density foam, you have to ease off the pressure or you could end up with a prune!

[danielfarley 0]

Female mold i take it? That could be a good way to go if your happy for me to use it! Could you give me the dimensions? Do you know what the profile of it is? and also a pic of what your ruder looks like? (my current design is a drop one.)

 

Thanks D

 

 

 

My mate used some of the rudder mould I have for WT on his 747, so that could work for you. Also, if you vacuum on to low density foam, you have to ease off the pressure or you could end up with a prune!

[Guest]

Hi daniel.

 

Pprobably telling you how to suck eggs here... but

 

i would suggest that before you make a new one you should do the following...

 

1. Understand why it broke. to me it looks like the location pin "hole" has been it weakness. probably water ingress?. Do you want to use the same pin system?

 

2. Also there seems to be inadequate glass laminate structure either site of the timber core at this point. Is this point of failure in the water, or beneath the rudder case/box?

 

3. When using timber as a core (especially laminated) most people will use less glass laminates and rely on the core timber to provide strength . Then when the core is compromised there is not enough glass either side and failure occurs. With a foam core the glass laminate either side of the high stress /sheer areas (such as the area just beneath the rudder case and the area around the waterline) is critical and most composite engineers will beef these areas up with unidirectional / tri axials....

 

4. Also when some production builders were building rudders in the 80,s and 90's they were just using the same chopper gun to apply chopped strand to these rudder as they would to the boats (female moulded).

 

5. IMHO i would carefully note the internal dimensions of your rudder case/box arrangment and ensure the top of the rudder fit very snuggly in there to start with - then build the lower part (all from the same foam blank)of the blade to the best shape for your design yacht. Foam should be spec'd correctly for the job maybe h100 or more but have a yarn with the guys on this forum as to the layups they use for similar type boats.

 

6. Best way to shape foam (if you have no CNC shapeing/profiler "mate") is to take your shape dimensions (depths at specific points) and transfer them to the foam then router along these depths. then use the router "grooves" to electric plane down too. For areas where extra laminates are required just use the router to the depth requires (laminate supplier can provide those)

 

Also, as mentioned already, if your loadings are very high (weather helm) then a spec should be drawn up but that will probably cost. A local boat builder who deals with this stuff all the time and has built composite boats / rudders etc will have enough experience togive you very good advice.

 

Finally, yes you have to buy a whole sheet when dealing with suppliers. ring around Boat builders who build composite boats and see what off cuts they have. If your blank need to be. for example, 50mm thick you can buy 3 lots of 20mm and glue together if you have to. (or any other thickness variants)

 

This is a very basic explanation and you may already be well on top of this but i hope it helps.

[danielfarley 0]

Hi Sir,

 

Yes, water ingress appears to of been a contributing factor... although it is more just over stressed numerous times... the wooden spare has crack's in it that are both old and new so you can see it has been slowly failing...

 

I plan to make the new one with out the pin system and with out a wooden core. As you said this was a ruder made with just chop strand and i will use lots of uni directional in the direction of strain.

 

No i dont have a CNC friend, what do you think about hot-wire cutting though?

 

Do you have any suppliers you can recommend talking to about foam, i have just talked to the core cell distributors so far. http://www.gurit.com/corecell-mfoam.aspx

 

 

Thanks for the advice.

D

 

 

Hi daniel.

 

Pprobably telling you how to suck eggs here... but

 

i would suggest that before you make a new one you should do the following...

 

1. Understand why it broke. to me it looks like the location pin "hole" has been it weakness. probably water ingress?. Do you want to use the same pin system?

 

2. Also there seems to be inadequate glass laminate structure either site of the timber core at this point. Is this point of failure in the water, or beneath the rudder case/box?

 

3. When using timber as a core (especially laminated) most people will use less glass laminates and rely on the core timber to provide strength . Then when the core is compromised there is not enough glass either side and failure occurs. With a foam core the glass laminate either side of the high stress /sheer areas (such as the area just beneath the rudder case and the area around the waterline) is critical and most composite engineers will beef these areas up with unidirectional / tri axials....

 

4. Also when some production builders were building rudders in the 80,s and 90's they were just using the same chopper gun to apply chopped strand to these rudder as they would to the boats (female moulded).

 

5. IMHO i would carefully note the internal dimensions of your rudder case/box arrangment and ensure the top of the rudder fit very snuggly in there to start with - then build the lower part (all from the same foam blank)of the blade to the best shape for your design yacht. Foam should be spec'd correctly for the job maybe h100 or more but have a yarn with the guys on this forum as to the layups they use for similar type boats.

 

6. Best way to shape foam (if you have no CNC shapeing/profiler "mate") is to take your shape dimensions (depths at specific points) and transfer them to the foam then router along these depths. then use the router "grooves" to electric plane down too. For areas where extra laminates are required just use the router to the depth requires (laminate supplier can provide those)

 

Also, as mentioned already, if your loadings are very high (weather helm) then a spec should be drawn up but that will probably cost. A local boat builder who deals with this stuff all the time and has built composite boats / rudders etc will have enough experience togive you very good advice.

 

Finally, yes you have to buy a whole sheet when dealing with suppliers. ring around Boat builders who build composite boats and see what off cuts they have. If your blank need to be. for example, 50mm thick you can buy 3 lots of 20mm and glue together if you have to. (or any other thickness variants)

 

This is a very basic explanation and you may already be well on top of this but i hope it helps.