Roberts Spray 36. Too slow?

Discussion in 'Sailboats' started by DennisRB, Apr 11, 2010.

  1. DennisRB
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    DennisRB Senior Member

    My friend just got a steel Roberts Spray 36. On first looking at the yacht it appeared as though it wouldn't win many races with a large beam, massive stern and trawler like hull shape. Its very roomy inside though.

    It motors around 3K with a new 50hp volvo. Under sail in 15K winds with large furling genoa and full main its lucky to do 3-4k on a reach, and it certainly doesn't point well either. It maybe does 4K on a broad reach with 15-20K winds.

    Is this to be expected with such a design? Do more streamlined steel yachts much greater sailing performance? These speeds might be bearable as a live aboard where comfort is more important than speed, but when you only have a limited time per year to go places you wont get far.

    Thoughts?
     
  2. bistros

    bistros Previous Member

    Dennis:

    Welcome. See the Slocum's Spray thread for more thoughts.

    To answer your questions directly, yes and yes.

    People's expectations and impressions of designs are individual and can vary dramatically from one person to the next. What I think is great may be horrible to the next person.

    --
    Bill
     
  3. DennisRB
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    DennisRB Senior Member

    I like sailing therefore don't like this design. We tried to make a 20nm passage in this boat from Yamba to Balina and had 24h to do it. The wind was 15-20k in favorable direction and we hardly even moved against the East Australian Current. When the wind died to about a steady 12k, I turned back for fear of the wind dieing totally and not being able to motor back against the current. Also it felt very wallowy even under full sail in 20K winds. Normally a yacht picks up speed and smooths its motion to a comfortable sway in sea. This really didn't feel good at all, probably because of the low speed compared to the size of the yacht? Not my bag.

    Thanks for the link. I read it all and it seems to confirm my thoughts.
     
  4. BATAAN
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    BATAAN Senior Member

    How to screw up a design

    Oh boy more SPRAY stuff. See the photo for a modified SPRAY that motored at 6 knots on a salvaged SABB 16 hp lifeboat engine for twenty years and now does the same, just in a little more headwind, with a now 10 year old 30 hp SABB.
    The difference in powering is I think (after fiddling with this one for 30 years) BERTIE has her prop on the port side, shaft angled at about 12 degrees from the keel axis, in very clean smooth flowing water. There is no centerline aperture or rudder in the slipstream that can eat 60 percent of your effective thrust. BERTIES's underbody and rudder are very carefully faired and eased so she sails better than many modern boats her size, because the rig is as big as it's supposed to be for the type. What you may think of as a large genoa is not really an effective driver for this type of boat and the marconi mainsails they put on them they look like caricatures, something out of a Mickey Mouse cartoon. Workboats need the sail area they were originally designed for because square feet equals power and the wide hull needs lots to push it.
    Also Roberts' boats have FAR too much freeboard in their most "Winnebago" extremes, and freeboard equals drag, which sucks power from the equation, again making you go slower all the time, especially in a head wind.
    Roberts knew a little enough to be dangerous, took a very mature and sophisticated design he didn't deeply understand, and managed to really screw it up by trying to use modern concepts. Poor motorboat, poor sailboat but makes a great "drink-aboard" at a dock somewhere warm.
    BERTIE on the other hand is one of the best short-handed passage making boats under 60 feet I have ever known. We did 2300 miles in 21 days, hard on the wind in the NE trades from Baja to San Francisco in 1996.
    The hull isn't so much your problem I think. 50 horse with the right prop and pitch should give 6.5 knots, so maybe something's wrong there. Also they sail well with a 1000 sq foot mainsail like the one in the photo, wonderful in light air, and easy to handle in force 9.
    Also is there a foot of barnacles and weed hanging down? With its huge wetted surface the type is VERY sensitive to the difference between a clean hull and dirty, even a seeming small amount. See page 5 of the SPRAY thread for a through briefing on the design.
     

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  5. Milan
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    Milan Senior Member

  6. DennisRB
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    DennisRB Senior Member

    Bataan. I must say your spray is a very beautiful yacht. Is she steel? What is the weight and length? Our one is 13T and looks to have half the sail area. Bertie seems to be made the way these yachts should be, our one is a lump. I have started a thread in the power section to try and figure out why she is so slow under power. If you can hit 6K with 18hp we have some serious probs if we are hitting 3k with 50hp!!!!! It does have a few barnacals growing, but nothing major.

    Milan, thanks for the links. I will take a look. Most of the yachts I can afford will be over 20 years old. Are older steel yachts with good performance common? What are some common ones I should look out for?
     
  7. daiquiri
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    daiquiri Engineering and Design

    50 HP @ 3 kts is outside of any propeller chart I have, there must be an error there. What props do you guys have installed?
     
  8. BATAAN
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    BATAAN Senior Member

    Bertie

    Bertie is 1 3/4 Port Orford cedar planking on sawn PO cedar frames spaced 12" on centers, sided 6" and molded 8" at the floors and 4" at the head.Deck is 2" douglas fir on on 4x6 fir beams. Very heavy stout wood construction. As far as your powering problems go, the relationship between prop diameter, prop pitch and available clean flowing water controls the actual power put into the water as thrust, not so much the power of the engine. Of course it's how much of the 50 hp goes into pushing the boat forward and how much goes into turbulence and inefficient losses. The prop should fill the aperture with say 2" clearance to any tip to prevent cavitation, prop should have proper pitch (if you tie the boat up, give it full throttle, it should remain under proper load with the engine working hard but not lugging down from too much pitch or revving freely with too little. This is a rough indicator of any pitch problems.
     

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  9. BATAAN
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    BATAAN Senior Member

    Off Center Thrust

    Here's BERTIE's powering "interface" that puts the HP in the water. As you can see very little turbulence, almost all thrust.
     

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  10. DennisRB
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    DennisRB Senior Member

    I read your big "rant" in the other thread. Quite an interesting read. :) I like seeing the pics of Bertie. That last pic shows light wind conditions yet the boat seems to have some lean and good forward speed. Under those conditions our one would be doing 2k.

    RPM always goes to 2400 (3000 is max rated for the engine) when fully loaded in the open water or held captive in the docks. There is hardly any difference is this good or bad? What does it mean?

    I am not sure what the prop is. We need to swim under and check it out. I hope its almost a solid lump of marine growth or something simple like that.
     
  11. daiquiri
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    daiquiri Engineering and Design

  12. Milan
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    Milan Senior Member

    It depends where are you searching. They are VERY common in The Netherlands, (steel boats heaven, probably more steel yachts then rest of the world put together), quite a few in France, also Germany, Belgium, but much less in most other countries.

    Have a look at Dutch adverts:
    http://live.botenbank.nl/nl/zoeken?cat=1&rompmateriaal=2&foto=1&sort=3

    It is only in Dutch unfortunately, but you will understand basics. (Steel is staal en sailing yacht is zeiljacht. Prices are in Euros).

    From what I heard, in your part of the world, (well, in the neighbourhood :) ), Denis Ganley was maybe the biggest promoter of steel boats. Many where built. http://www.ganleyyachts.co.nz/index.html

    Then there is Graham Radford, Adams, some were built to Spencer designs ….
    http://www.radford-yacht.com/
     
  13. terhohalme
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    terhohalme BEng Boat Technology

    Is the bottom like a coral reef?
     
  14. BATAAN
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    BATAAN Senior Member

    No power

    If the boat was even half way engineered it should go 6 knots under power. You mentioned being in a strong current which could be a large factor too. I wasn't there but here in Pacific NW there are many places with 9 kt currents at certain times. Since I can go 6 when all is good I would be doing 3 kt backwards. I assume that with the huge masses of water involved there can be locally very strong currents in passes and such and maybe you weren't allowing enough for the current. Consult tide tables for the area at the time and you'll know more. A Roberts Spray is a perfectly good and viable boat, it just takes a lot of power to move. The rig should be big enough that you have to reduce your working sail at 8 to 10 kt of wind. On Bertie this is when we just drop the mizzen and and furl it. To make power and drive us along on any point of sail, the bottom of the "engine" we call the sail should start as low to the water line as possible without making a boom that kills people to give as large a sail as possible on a given mast height, which on SPRAY types with their barge-like stability curve, must be kept within limits. SPRAYs will set a huge sail area safely only you keep it low and long, thence the original long bowsprit and overhanging boom on gaff sloop version. On the Roberts boats the deck has been raised, therefore the room between deck and boom is less, so they raise the boom etc, throw away the gaff, set a three sided handkerchief of a main, spend a great deal on a roller furling headsail, which is delicate and always up providing windage when you don't want it (force 9). This all means the sail and its power are smaller while the deck height and its great aerodynamic drag has been increased, thereby reducing the power and increasing the drag, so a good boat gets turned into a less good boat. On the other side of the coin, on a Roberts boat with a raised deck, if it's knocked down flat the greater immersed cabin volume is in exactly the right place to greatly increase the righting moment and the recovery. From experience, you sail these boats on their bottom, as you would a scow, it's the same in extreme conditions too, she will stand up and thrash it out when vessels of lesser stability are sliding off to leeward.
     

  15. DennisRB
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    DennisRB Senior Member

    That thread was supposed to be regarding the power side of things only. This thread was supposed to be be about sailing. I don't know if people in the sailing section know all that much about the power side of things, or if the people in the power section would know much about the sailing side of things and I wanted to expose the correct people to the relevant questions.

    Thanks Milan. I will take a look. Australia seems to have quite a few steel yachts too. I see many in various states of repair in any marina.

    Bataan. Me speed figures are through the water, not over land. You mention righting movement. Yours does not carry external ballast does it? Would yours be doomed it it ended up upside down and how would this compare to a Roberts Spay with its weighted keel? I hear what you are saying about the sail area. The sail area is much too small on this boat going by yours. This isn't an easy or cheap fix. It would probably double the price of what we he paid for the whole yacht to get his right. It didn't even come with a spinnaker.
     
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