Martin Brooking

Brilliant question Stephen and very clearly stated. In practice the class associations and MYA could introduce an accreditation process for sail makers. It doesn’t have to be complicated (like you I’m totally confident that our regular sail makers know exactly what they’re doing). So the sail makers themselves could devise something practical and reliable. That way accredited sail makers can supply accredited products. Some may argue that SMOD classes like ILCA (laser) have had instances of out-of-class sails and spars. But these tales are mostly apocryphal; and it usually only matters in big events (which like our sport, are usually subject to scrutineering).

Hi Andy, you probably know this already, but I’m still a keen and active dinghy sailor/racer. I still prefer Sunday club racing in my dinghy, so Sunday radio yachting events are out for me at present. Other family commitments (grandchildren) can restrict Saturday availability too. The above is bound to change over time.

Hi Brad, thanks for your reply. Yes, the behaviour of masts and rigs is a complex topic. My background in ship science and a lifetime in naval architecture does lead me more towards the science and engineering (and not always for the better!); and I totally agree there’s no substitute for hard-earned experience. Aluminium alloy is a complicated material to use and the hardening process complicates it further. As far as I know hardening doesn’t change the elasticity (Youngs modulus), but it can significantly increase the strength. So a hardened section doesn’t become stiffer, though it does become stronger. Any aircraft engineers out there might be able to help on that one - they’ll know quite a bit more about aluminium than a naval architect! There are several different manufacturing processes for tubes and mast sections, and production varies a lot. Manufacturing tolerances also lead to variations. The hardening process is also very variable and these together can lead to uncertain qualities of tube. In ship construction it’s standard for structural materials to be tested and certified against set standards such as classification society rules, so that the material properties are categorised and verified giving confidence in the materials used. Of course we don’t have that level of information for dinghy or model yacht components, so it’s a bit of a minefield. I’ll stop now. Sorry if I rambled a bit off the original topic. There’s a lot more to add about cold work hardening and other thoughts, but that won’t help anyone’s boat go faster! Time on the water is a much better idea.

Hi David, I’m afraid I don’t have enough knowledge of IOM history to know whether they had spreaders from the get-go, but the class rules list them as optional items, rather than mandatory. The B rig mast is quite a bit shorter, so the bending of the mast would be less than for an A rig. I would think the location of the mast in the hull is quite important - especially restricting any free movement at deck level, as this can make a big difference in how much the mast will bend between its base and the shroud points.

Great discussion! Sorry if this next point is a bit nerdy, but in selecting the right type of aluminium tubing for a mast, it’s worth bearing in mind that the tensile strength doesn’t have much bearing on the stiffness of the tube. Basically the tube stiffness depends mostly on two things: 1. The section dimensions (particularly the 2nd moment of area) and 2. The Young’s modulus of the material. I understand that different grades of aluminium have widely varying strengths, but surprisingly very similar values of Young’s modulus (about 70 GPa, give or take). In practice, this means two tubes of different alloys with identical sections (e.g. outside diameter and wall thickness) may have different strengths, but their stiffness will be pretty much the same. By the same token, you might select a very high grade of aluminium tube, with a thin wall thickness to save weight, but a lower grade alloy with the same outside diameter and thicker wall (to give equivalent strength) will actually be stiffer, because the section will have a larger 2nd moment of area (but of course it would be a little heavier). Again apologies if the above sounds a bit nerdy, but sometimes buying expensive materials doesn’t always have the outcome you’re hoping for! BG is absolutely right; if David’s B rig mast has a large section (diameter/wall thickness) and is well located in the boat, it may be adequately stiff without spreaders. It just needs to be tried out on the water.

Thank you Andy for persevering with this - and thank you to everyone who contributed so diligently. It seems we now have a definitive answer (though I sense another intense bankside discussion coming on😉). I still mostly sail dinghies; and usually they’re much bigger than a starting mark, so perhaps there’s less controversy. But for radio yachts the diameter of a mark might be almost half a boat length. So Andy’s original question is an important one and I’m relieved it’s been answered! We’ll still have claims from boats called OCS that they were not over the line, but at least we can now agree on which line is the correct one to use.

Hi David, Ah yes, I fully understand your points - I’ve been there too (some would say I still am!) and I’m no whiz with electronics either. But as I understand things, your current winch will turn at a certain rate (i.e. turns per second); and so a smaller drum will proportionally reduce the sheeting speed too. Have a fiddle with your transmitter - hopefully you’ll be pleasantly surprised. Having said all of the above, removing the winch drum is not usually necessary all that often, so maybe you could just carry out whatever maintenance is required, refit the drum and carry on sailing? M

Hi David, I guess the most obvious effect will be that you will reduce the range of the sheet travel roughly in proportion to the reduction in diameter. I believe the important diameter measurement is on the bearing surface of the drum, not the extreme diameter. You may be able to compensate for the reduced travel by using the adjustments available on your transmitter - and maybe you can try that out fairly easily before you remove the drum? A new winch might feel like a step too far, but there good are advantages to having a quicker winch. I have an RMG on my current boat and although it’s not the quickest it is more than adequate for club racing. The new Red Ant winches look interesting…. would be nice to hear from anyone who has one. M

Hi Eric, that’s a great summary. Thank you for replying so comprehensively. I’ve gained a much better understanding over the course of this thread. There is a well stocked angling store only a mile or two from my home. Armed with the above I’m going to check out what they have available. I’ll report back if I find a good looking product.

Thanks Stephen. I believe that's 4-strand, which is interesting. I think the lines I have are 8 strand (though really not sure). It will be interesting to compare and to see how your new rigging fares.

Good news Stephen! Can’t wait to see the boat on the water again. 80lb spectra … what is the brand and where did you source it? Hopefully if the boat’s ready on Saturday I can compare the cord you used with the heavier cord on my other boats.

Thank you John that’s very helpful. I see the rigging guide is fairly generic. As far as I know there are many different types of dyneema and many more different brands. I think it’s used by anglers too and I didn’t know if it was a good idea to explore their products. I was hoping someone might have some specific recommendations of readily available products. Thanks again M

I sail DF95s and IOMs and I’m hoping for some advice about choosing the best general cord for the lines. I do have a small supply of the standard thin dyneema that came with my 95 when I bought it in 2016 (yes, it’s an early boat). My wife’s 95 and my IOM were bought second hand and both have slightly heavier braided lines for sheets and standing rigging (on the 95 only). This line, though slightly thicker, runs well and has the benefit of being easier to tie - it seems a bit easier to adjust bowsies too. It’s also pretty robust and resists wear very well. Whereas the standard 95 line does fray quite easily and is a bit jerky with the bowsies. Sadly I don’t know what the heavier line is. Can anyone advise on a type/brand of good general purpose line please? And where is a good source? Thanks and regards to all

Hi Stephen, I haven’t used that supplier, but I have bought Vapex products - either from Mike Weston or from Amazon. For me, both of these have been very reliable. If you have Amazon Prime the obvious advantage is free rapid delivery (sometimes at a slightly higher price). Mike is very reliable and has the advantage of knowing DFs inside out! Martin

Hi Craig, Many thanks for your post and thoughts. I appreciate it because I'd really like to see more of this type of discussion on the forum. There's a lot of knowledge and experience out there and the forum is a great opportunity to share that. Is the photo you showed your latest boat? It looks fantastic and the finish is excellent. If you have time it would be great to see photos of your various builds and if possible a few thoughts on how and why you modified each successive boat and whether or not you thought the modifications were successful. There are a lot of different designs at my local club and it seems that as long as it's a metre long, pointy at both ends and displaces no less than 4kg, it gonna work ok! I've figured out that hull design, though important, is only a small part of what makes a successful IOM. The rig set-up makes a massive difference and of course a good skipper, who can adjust the boat (and himself) for the conditions of the day probably has the biggest impact on speed. I bought a Widget (early flat-deck design) as my first boat just under a year ago. I probably didn't give it enough time, but I became frustrated at how easily it would 'go down the mine' in gusty conditions when other boats were not. I wonder now, whether this trait was due to the flat-deck design having the rig set too high in the boat relative to similar boats with a 'vang well’, but most likely it was my lack of experience in setting the boat up properly. I bought a Lintel late last summer and have been really impressed with it's heavy wind performance against some pretty decent club competiton. My wife bought an Italiko from an elderly club member who was giving up radio yachting. Like the Lintel, this boat doesn't have the up-to-date lines of a modern narrow design, but in light to moderate conditions the Italiko has a very decent performance. I think you’re right about the risks of the bow design on my new build, but as you say the boat can easily be modified after it's built - and it's not such a big deal to make another hull if I need to! For me, this is an opportunity to indulge my interest in naval architecture and have a bit of fun. Your observations on hull design are really interesting and I'm looking forward to learning more about this in relation to IOMs as my experience progresses. I've been away for a few weeks and have made no progress at all since posting the photos. My next step is to buy some resin and cloth to get on to the next stage of the process. I can't wait to see it on the water and continue the learning process!