1982 Cherubini w 12 HP Yanmar - Hull Speed?

Discussion in 'The Cherubini Hunters' started by polarbear, Jun 25, 2018. Add this thread to a FAQ

  1. kloudie1


    Joined Nov 6, 2006
    8,287 posts, 753 likes
    Hunter 34
    US Mandeville Louisiana
  2. FastOlson


    Joined Apr 8, 2010
    1,082 posts, 151 likes
    Ericson Yachts Olson 34
    US Portland OR
    I just took a look at the design as presented on Sailboat Data.
    Disp. is 10600 (exactly the same as our 34' boat), but the DWL is 27 feet, and there is considerable IOR-ish tuck up to the stern. No surfing. (!) The speed under power might be more like 6.5 with the referenced size diesel. Not bad.

    Pushing more HP into the water will not get you much more speed with that particular hull form. Of course some more HP is nice when you have to motor into a steep chop in a narrow channel.
    It's a moderate hull with classic good looks, compared to the current crop of "floating RV's with masts!"

    One other bit of YSM12 trivia: if you do not push it to the stop, fuel usage will be about 1/3 to 1/2 gallon per hour. That is a very thrifty engine!

  3. Pizzazz


    Joined Sep 11, 2015
    101 posts, 31 likes
    Hunter 31
    US Marina del Rey
    I have a H31 with a 25 ft waterline, hull speed calculated at 6.9 knots, 9700 lb design weight, heavier now.
    With the original 2GMF, 13 hp, it would do 6.2 knots in flat water, closer to 4.5 knots against wind and waves.
    Currently, I have the 2GM20F, 16 hp, it would do 6.5 in flat water and above 5.5 knots against wind and waves.

    Based on the above, you should be doing around 6+ knots in flat water 4+ knots against wind and waves. You should be fine but if the weather is bad and you happen to be in a high current area, you may need to be more careful.

  4. sandpiper10471


    Joined May 31, 2007
    708 posts, 6 likes
    Hunter 37 cutter
    CA Blind River
    My former 33 (1980?) had a 2 QM15. Pushed her at about 6knots in flat water but if I were bucking big waves and strong wind, speed would often drop to barely above steerage. Two bladed fixed prop. Three would have been better. However, rule of thumb indicates 1 hp for every 500 lb.displacement. Therefore, the 12 hp is very undersized, the 15 was barely adequate and something around 22 hp would be so much better. On the plus side of things, the 33 is very easily driven and sails incredibly well, especially to windward ( deeper draft model).

  5. billyt14607


    Joined Dec 10, 2012
    14 posts, 1 likes
    Hunter 33.5
    US Rochester, NY
    What do you have for a prop? We have a 1990 Hunter 33.5 with a 2GM20 engine and we get 6.5 knots on flat water no wind and 5.5 knots into a 15knot headwind 1-2' waves, yes they are underpowered, later models had a 20hp motor.

  6. lillia28


    Joined Jul 22, 2011
    140 posts, 26 likes
    Mariner Yacht Co.(NH) Mariner 28
    US Atlantic Highlands, NJ
    The YSM 12 is a big single cylinder, slow reving engine. It produces a LOT of torque. If you compare the specs, the YSM peaks between 3,000 and 3200, the newer higher hp engines peak at 3600 or higher. I would sail the boat and then decide. Torque moves boats, horsepower sells engines.
    I have not seen torque specs on the YSM 12, but seat of pants, it is fairly powerful.
    YSM ownership is a love /hate relationship. Reliable, powerful, economical but will rattle any loose fillings out of your mouth. They didn't call them YanHammers for nothing. Still and all, after sailing with Thumper for a while, you develop a lot of respect for it. If its a new to you boat, sail it for a while before you start on figuring spending a lot of money to replace a running motor. I'd consider a 3 bladed prop before I jumped to a re-power. Unless you are planning on keeping the boat for longer than forever, the economics of a re-power are against you.
    And few experiences equal the transition from power to sail when you shut down a YSM 12!

    FastOlson and Will Gilmore like this.
  7. azambella


    Joined Sep 27, 2008
    12 posts, 1 likes
    Hunter 33
    US salem
    Our H-33 also has the Yanmar 2GM (fresh water cooled). After a lot of questions we decided to
    change the propeller.

    This provided unbelievable performance improvement. We went with the 3 blade
    sail propeller from Michigan wheel (sailor 3).

    I will have to check my notes for the size & pitch etc.
    Everything smoothed out and it absolutely increased speed.
    All that said, the motor is tiny for this boat but it works very well as aux power.

    lillia28 likes this.
  8. lillia28


    Joined Jul 22, 2011
    140 posts, 26 likes
    Mariner Yacht Co.(NH) Mariner 28
    US Atlantic Highlands, NJ
    My Apologies, I had the YSM single cylinder in my head.The 2GM is a newer 2 cylinder design. Newer than the YSM any way. Some of what I said is not relevant to the 2GM, a fine engine but not a torque monster like the YSM. That being said, a 3 blade prop may be a more economical solution than a repower. Sorry for adding to the confusion.

  9. tango_51


    Joined Dec 29, 2014
    13 posts, 2 likes
    Hunter 33
    US Dallas
    Interesting conversation I had the same dilemma with my 1982 Hunter 33 with a 2GM 13hp motor, which is some what under powered for some conditions, so to solve the problem without spending a huge amount of funds on repowering with brute force or throwing away a bunch of money on a none power boat (the point of a sailboat is to sail not motor) did the math calculations an came to the conclusion that changing the propeller to a 3 blade and incensing the diameter and changing the pitch was the thing to do... which worked!! wonderfully.. the prop walk is great know .. I have seen a increase in speed at the same rpm of about a knot and half and fuel saving when I do have to motor.. (clean hull helps as well). personal I like the 2GM its simple and easy to maintain KISS (keep it simple stupid) is my moto because things break!!! when your cruseing and the simpler it is the easier its is to fix at sea. (trust me been their done that, got a sticker for it)

    Will Gilmore and jssailem like this.
  10. dLj


    Joined Mar 23, 2017
    341 posts, 140 likes
    Hunter 30
    US Snug Harbor, Lake Champlain
    I wonder if that would also be the case for YSB 12. Although my engine and prop combination run very well right now, I have little reason to change anything at this point. I'd heard the old YSB was supposed to be noisey and vibrate a lot. Mine does neither. I do have quite a bit of prop walk though.


  11. Plymouth Sailor

    Plymouth Sailor

    Joined Dec 11, 2015
    176 posts, 32 likes
    Hunter 25
    US Plymouth
    I've been told by experts that a sailboat pushed with a motor will only go about hull speed or less. If that is your experience then the HP should be fine however I've also been told that more HP on a sailboat helps not with speed necessarily but with resistance i.e. current, wind, waves etc.

  12. dLj


    Joined Mar 23, 2017
    341 posts, 140 likes
    Hunter 30
    US Snug Harbor, Lake Champlain
    I can attest to HP helping with wind and waves. Not so sure about current though as that also is a function of how the hull goes through the water.


    Will Gilmore likes this.
  13. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    4,590 posts, 2,533 likes
    O'Day 19
    US Littleton, NH
    It is a function of bottom shape. Newer racing designs are easier to get up on a plane. Flat-ish bottom with less rocker = easier planing. All boats can exceed Hull Speed, it's a question of energy to return that adding more HP will give you. And yes. Big HP coupled with big propeller means better headway against opposing wind and waves.

    -Will (Dragonfly)

    FastOlson likes this.
  14. Mikem


    Joined Dec 20, 2009
    521 posts, 105 likes
    Hunter 466
    US Bremerton
    A good rule of thumb for displacement hulls is 5hp/ton.

  15. garymalmgren


    Joined May 29, 2018
    66 posts, 46 likes
    Canel 25 foot
    Jonathan jp Shoigama, japan
    And few experiences equal the transition from power to sail when you shut down a YSM 12!
    Truer words have never been spoken.
    BUT you tend to shut down and sail way before the boats with smooth quiet engines do.

    Back on topic. If you want to know how fast she will go under power, Fire her up and let her rip.
    That is the best way to find out.


  16. twistedline


    Joined Dec 24, 2011
    78 posts, 1 likes
    Hunter 33C
    US Chesapeake
    My 1982 H33 will do 6+ knots in flat water and clean bottom with the stock 2GM 15HP.

  17. Robert1224


    Joined Jan 22, 2008
    87 posts, 1 likes
    Hunter 30_74-83
    US Rochester, New York (Lake Ontario)
    My experience with a YSM 12, clean boat, two bladed prop, cruising weight, calm sea, and no wind was ~ 4.5 kt. Although I had burst over 5 kt on occasion, 4.5 kt was the number I could most often expect and the best one to use to plan for cruising. The condition of the YSM 12 was very good although the hours unknown.
    Cheers, Bob