I’ll pull this comment over to this thread:

luckystrike118 - 17 July 2014 03:04 PM

Hi Marco,
sorry, but my pm function does not work in the moment, so I post my answer here. It is no problem if you use quarter sawn (45°) wood for strip planking and for stringers as well.

And please please please please ... plan for a 2 to 4 hp outboard motor for your proa. Rowing is no solution for a 23 foot proa. The North Sea and the Baltic Sea is packed with buisy shipping lines and if you have only light wind you can not risk it to cross a shipping line and force a tanker to give you way. Not to think about if you have to reach a habour with a strong headwind and/or current ... and yes, there are currents in the baltic!!! And they run in the same direction 24 hours a day, because they are powered by the wind, no joke!

Yacht Habours these days are not made to be entered with sails. If you don’t believe me then come to Wilhelmshaven these days and go sailing with me for a weekend. I will allow you to row my boat and you will see that it is not practicable, not to say dangerous.

Best Regards, Michel

Hey Michel,

Throughout the whole development of the boat you’ve been really insistent in your recommendation of taking an outboard engine along. 😉 I really hate those iron topsails, and a light four-stroke 2.5HP outboard weighs ~14-15kgs, add a can of gas and we’re talking around 20kgs of extra dead weight when sailing though. You have experience at the North Sea coast though, I don’t, so probably you’re right about the engine. I’d love to take up your offer on some sailing at Wilhelmshaven to see for myself too, I’ll PM you. 😊

A quick update otherwise: progress has been a bit slow, been bogged down witha few other things and trying to find suitable lumber, but I hope to complete the mockup this weekend. 😊

Cheers,
Marco

Hey guys!

Progress was good this weekend; the mockup progressed quite a bit, and I made a fair bit of ground on a couple other fronts as well. I managed to do a bit of CAD work too, and found that increasing the boat’s length from 7.5 to 8.0m increased displacement at the same waterline from 500 to 600kg, which is hopefully enough to cover the weight of the boat, two people, and all the required gear. I was pretty surprised by how that increasing length and beam by ~7% and while keeping depth the same led to a whopping 20% increase in displacement, and while I haven’t checked out all the details yet, the slightly larger variant looks pretty good so far.

Where the mockup is concerned, I have to say that overall building it was a really good! I’d defintiely recommend it to anyone building a small cruiser like this, it’s already proved to be extremely helpful in working out design issues, and I’m just getting started. Loads of opportunities and potential problems which I hadn’t considered before are making themselves apparent now, and it’s really good for motivation too. 😉

I noticed yesterday for instance that without the deck, you can sit very comfortably on the pod floor, arms resting on the deck frames, which has me thinking that I could add two extra hatches, each just big enough to fit your torso through with some room to spare, into the deck above the pod. Then there’d be two seating spots, one toward each end of the pod, which could provide for soem quite comfortable seating when sailing in good weather, and better cabin ventilation. Keeping the hatches small is a structural thing, with a deck-stepped mast the loads on and in the deck are going to be pretty high (if the mast only has shrouds at the top, then there’s over 4kN = ~400kgs of lateral force on the maststep when sailing close hauled for instance), so I really don’t want to turn the boat into a convertible.

During a catnap in the pod yesterday I also found that my initial suspicions were right; it’s a tad too small and needs about 5-10cm extra width to fit me comfortably. Having the pod floor slope a few degrees down to leeward when the boat is level, doesn’t seem like much of a comfort issue, and the relatively limited height of the pod (about 65cm) isn’t an issue either, though getting in and out of the pod is a little akward (but fine), since you only have sitting headroom in the cabin to begin with.

And now to the pics…

Cheers,
Marco

Hey Rob,

am I interpretting the diagrams you posted correctly in that you are using two sidehung rudders? If so, do they kick up, are the cartridge rudders? Are both of them down at the same time? What kind of linkages or liens are you using to control them? Can the relative angle between the rudders be set, e.g. higher AoA on the front board if more lift is needed in the front to create more lee helm?

I was thinking about that a lot after sailing yesterday. Thus far I still don’t have any kind of low-draft steering / lateral resistance system for Firstborne, which I so desperately need for the Wadden Sea though (not for the other places I want to cruise though). Assuming your system can do all of the above, except perhaps the cartidge part (just kick it up part of the way then if you need to reduce draft), then I really really like the setup, since you can tune the balance of forces perfectly that way. A good symmetrical NACA-section has pretty good L/D values anyway, so the drag pentalty over an asymmetrical daggerboard is probably not so bad (provided you can set the AoA and aren’t dependent on leeway). You do pay a drag pentalty because they are surface piercing, but there’s no raising or lowering of boards when shunting, you don’t have to build trunks, don’t have to worry about collisions, you have a deep draft and shallow draft system in one, the hull is stronger, you can tune the boats balance all you like, and you can get away with 2 boards instead of my currently planned 4 + shoal draft solution, which is just kind of crazy…

What kind of a linkage system do you have there? What will the shunting procedure look like? And are you worried about the steering loads resulting from wave impacts on the rudders?

Cheers,
Marco

 

Marco, I have pasted your query into the Design and Concepts Forum, because I (and presumably others) can’t send or reply to PM,s (just one of the problems Michael was referring to in “The End of the Forum Road”) I hope you don’t mind…...

Sidecar will have 2 sidehung rudders with a casette framed on top but open at the back below so that they can kick back Gary Dierking style when you hit bottom, I intend to use both all the time, for precisely all the reasons you outline above. Shunting does mean swinging them through 180 degrees, Depending on the balance I want for any particular condition or set up, it might be that I will have to adjust the heights of each after each shunt. You could use just the rudders to counteract leeway, but I am going for the smallest rudders I can get away with because of possible steering loads and speed. I am not so worried about wave impact. And I will be using a foil in any case, albeit mainly for dynamic RM and “autoflight / dump”

PM me with your Email address and I can send you details of the setup.

Rob