"nARROW" - starting construction

Working directly with Claudio Diolaiti, and keeping in mind the “skinny” boats that are currently all the rage, he was kind enough to take his narrow deck design RG65 and draw up station shadows to allow a build of a new, lightweight ultra-thin design. The design, currently titled “nARROW5” was drawn to meet my requested criteria - being ultra thin, having chines, and having a rounded bilge to reduce drag in light airs, and slab side above the chines. The design he has put together has a maximum beam of 87mm and a waterline maximum beam of 84mm. He is proposing a total displacement weight of 1083 cm3 ! Not sure if I will be able to hit that target, but will give it a try.

If I run a bit “fat” during my build, I hope it will still provide me with an idea of the design, and it’s competitive possibilities. It may be that I will use the finished “wooden” boat as a plug for a future glass or carbon hull.

Claudio will, no doubt, want to add commentary to perhaps explain further his design - which I welcome. I was going to try to use a 500 gr. bulb, and he is suggesting a 609 gr bulb. Will see how it floats and if it is a very “tender” hull, I may try a slightly deeper keel…although it will all depend on how close to his suggested weights I can stay. Obviously I would love to come in less than projected and add some corrector weights to bring it up to his design specifications.

My plan is to post some photos as I proceed to stumble along. Since I am “almost” done with a major bathroom remodel, my time will be spent finishing that off first - so an early/fast build will probably not happen.

This is the design I was waiting for!! Looks that I will be following your build very closely, and maybe start my own build.

ClaudioD: Can you share the shadows, too?

I think the target weight is completely feasible using my fiberglass technique. MY RG65 displaces 975gr (complete hull 100gr, keel+bulb 662gr, rudder 10gr, A-rig 80gr, electronics 123gr) Take a look here http://www.rcgroups.com/forums/showthread.php?t=2098471

Having the winch sideways is strange… can be difficult to place/remove for maintenance.

Hope it all goes well!!!

Hi Tom,

Weight - as with all things Claudio does, he included a weight “budget” for all components, etc. You can look and then compare with your actual weights.

After discussion with Claudio about the winch, I (maybe ?) convinced him of “why”. If you look at pretty much all non-self-tailing winches outside of the r/c sailing community, it is noted that almost all are installed horizontal, and the cable feeds off the top of the winch. I will probably construct a different drum, one with higher/taller sidewalls and using a fairlead directly in front of the drum, see how it works. Both inhaul and outhaul should have no issues, since line is fed directly to the drum. Sheeting out in very light air will have less drag since line isn’t being held by any kind of tension spring/cord. Quite a few years ago, a friend from the UK suggested making a small balsa “box” in which to collect the mainsheet if it has a tendency to hang down without tension from the mainsail. That option is still a possibility. Keep in mind, that there were “string-eater” winches, that just spooled in on one side of drum, and spooled out on the other.

The winch mounted horizontal on a board will plug into slotted upright posts - similar to the way a computer memory board plugs in. This would allow an unplug of servo wires, lift two catches and simply draw the winch up and out. Eliminates fooling with 4 of those tiny mounting screws if a winch servo swap is needed to be done in a hurry.

Claudio was going to post the design, and I am positive he will share. He has several different frame drawings depending on type/desire of construction techniques. My only change is that one inside hull stringer will still run in line with the waterline while the upper “external” stringer will be located at the “break” between hull and sides - making it a hard chine… at least to start. His templates also show a deck, bow - but one would have to split hull horizontal to build deck at same time as hull - so I will build the deck, separate from the hull - then join together. Building with a vertical hull split as you did with your fiberglass hull can be accomplished exactly as you did it - two half hulls with deck and join along keel line.

I know he is still unpacking after his move/relocation, so may not have a ton of time to stay up-to-date on forum topics.

Stay well, and let me know if you have any other questions.


Take a look here for a good discussion on drums and sheeting designs for RC sailboats. http://www.onemetre.net/Build/Drums/Drums.htm

Summary for me is: chose one of these two designs. None of these require fairleads or boxes around the drum. You can just leave the drum open and the lines running free, as the line on the drum is always in tension

I’ve used both, and prefer the Open Loop with elastic, like I did in my RG65 here (the elastic is a piece of latex rubber):

Hi Dick and Tom, please find the n/Arrow5 drawings in attachment. There is a printing error about the bulb weight, it should read 675/683g and not 609g. Simply the bulb weight is the difference between the full displacement of 1083g and the construction weight. Before is too late Dick, I shall confess that a doubt is running in my mind : Chine or not Chine ? Until now my RG65 exhibited a draft of 32mm while the n/Narrow5 is 42mm therefore 10mm deeper. Of course nothing for nothing !! My question : Is eventually the deeper hull behaving already well enough against lateral drift to avoid to additional flat surface as the addition of a chine ? You have here the two options, shadows are at 100% scale. Cheers ClaudioD

Hi Claudio -
Thank you again for making drawings/lines available. Maybe Tamstro will have a faster build then mine - [smile]

I am giving thought to using the chines - for the following reason.

When going to weather, the hull is heeled from 5o to maybe 40o all depending on wind conditions, strength, gust and ability to see the angle of heel from a distance. (I understand your 30o being optimum). One major factor in sailing to windward, is the ability of the hull to prevent as much leeward drift as possible. Since a nicely rounded underwater section allows a lot of side slip, I want to see and use the chines and “slab” (vertical) side to prevent slip as much as I can. With minimum heel (light winds) the boat should have minimal slip and be as fast as other boats, but when the wind provides a degree of heel then it is a hope the flat sides and chine will reduce the side slipping by providing more lateral resistance. In fact, I took a pencil to your sectional drawings, and drew in an oversize chine - one that creates a “step” that extends outward slightly from the hull. All in an way to keep water from flowing easily from the side (lateral resistance) to the rounded bottom of the hull. Not sure I will build it that way right now, but it would be simple to “tack glue” a hard square (or maybe rectangular) strip of wood along the designed chine line, to disrupt the flow from the immersed flat side to the rounded hull bottom.

Strictly an idea and thought at the moment. I remember my dad’s outboard power boat which used a “3/4 inch -about 19 mm - quarter round” strip of oak molding along the length of his waterline. It was primarily there to reduce spray - but also acted as resistance when turning sharply when under power.

Will be interesting to see which design Tamstro will elect to build to. Perhaps tonight I can visit garage after wife is in bed, and cut out the station templates. My bandsaw doesn’t make much noise. :wink:


Hi Dick,
not sure it will work the oversize chine because lack of sufficient speed… anyhow is worth trying !

Thanks a lot, Claudio!!

Need to convince my wife to let me use the kitchen as shipyard, again!

One question: all your plans have an overall lengTH oF 650mm (including bumper). But the RG65 rule says the hull can be 650+/-5mm (plus a bumber of 5+/-1mm)

So, why do you not use all the length allowed by the rules?

Hi Tom,
being 65cm or 66cm overall, will not change very much. In my drawings the bumper is of 8mm thick and not 5mm included in the 650mm overall length. Probably was an old rule !
The water line is immersed for about 5 mm at the bow and similarly at the stern. This feature will produce an artificial increase of the dynamic LWL length.
If you wish to make a hull of 655 mm, is sufficient to place each shadow at 65.5mm distance including shadow O.

If the Rules do not make mistake, is not anymore an RG65 but rather an RG66. see image

Is some one interested to verify the Rules Validity ?


Claudio: look at the diagram in Appendix 1. It is very clear regarding bumper being outside the 650mm!!

This has been a topic of discussion for years between RG65 sailors, but the rules haven’t changed. I got versions 2010 and 2014 myself, and the are the same!

Yes of course, this means also that the boat length is varying from a minimum of 649mm to a maximum of 661mm. Tolerated variation = 1.84%
In my opinion should not be since the max boat length is supposed to be considered as the LOA -Length Over All.
But everybody knows that the world is not perfect !!!
If the same principle would be applied to a Class M the difference could be as high as 2.37cm and this start to count !!!
Anyhow I will stick to 650mm LOA.

I would rather be on the short side of the argument.

Then - if racing, there is no question as to being legal — and eliminates protests, etc. My son-in-law’s boat was built to fit on a shelf in family room when not sailing, and without a bumper, it is almost 1-1/2 inches too short (almost 4 cm !) Not sure “why” there is a minimum length, and if waterline length is a judge of boat speed, then I am providing my own performance limitation! Since he doesn’t race, it was made shorter on purpose and by his request. I suppose if racing was desired, one could use double-sided tape and add a foam block to transom plus a bumper to bring it closer to 65 cm.

Boat in question is the “Dirty Deeds” - black hull/sails with photos of it elsewhere in the forum.


Hi Dick,
for sure will be difficult to race against RG65/66, pity that the RG61 does not exist yet ! heheh !!

BTW I added at post 5 the shadows drawings at scale 1:1 ready for cut for both n/Arrow5 and n/Arrow3.


PS: the .RAR files are not accepted, I was obliged to collect all shadows drawings and convert them to .Zip file.

Claudio - I remember opening some RAR files, but then also remember you sent them to me via email.

Regarding the files you recently posted back in post #5, were there any significant changes from the stations you emailed to me? I took those that I received in your email and created my cutting stations (for chines) and want to be sure there are no other changes?

Thanks, Dick

These are (a few of) the shadows sent to me via .RAR file format. If no major changes, I will proceed with cutting templates and prepare to mount to building board.


Hi Dick,
fine !
the .RAR file are OK via mail of course, but not with this forum with ‘manage attachments’.

Review of general plans considering the Rule of 650mm + Bumper.
See attached plans

Great Claudio!

I sat down today to start building the nArrow5, and found two construction problems:
[li]I do planking with 3mm balsa, and it’s difficult for me to substract 3mm all around the shadows.[/li][li]My jig has only 6 shadows, at 0-130-260-390-520-647mm (last one 3mm less to allow for 3mm shadow)[/li][/ol]
Is it too much if I ask you for plans with 6 shadows and 3mm spacers? In the meantime will start getting materials for a new 11-shadow jig.


Tom - the plans (.RAR) files that Claudio sent me included 10 stations plus station “zero” (bow).

If you download a free file … 7-Zip it will let you open the .RAR files in PDF format. I’ll be happy to email you those files. PM me your email address if you want that format.

Cheers, Dick

I Tom,

I could do it, but requires some time since it is like to design a new model. How long could you wait ? heheh!!

The reason of 10 shadow is due to the use of 2mm stripes as asked. To avoid flexing during sanding is better to reduce the shadows distance.
This is particularly valid when the hull is wood planked like red cedar or mahogany. To reduce weight overall is better to reduce the thickness and therefore distance between shadows.
My support below used for all model sizes up to 1400mm


Hi Dick,
at post #5 are also available the ‘PDF’ files for n/Arrow5 shadows to scale 1:1.