Jim, the basic hull speed equation is 1.34 x the square root of waterline length. Take an m15’s 13.25’ waterline and you get 4.88 knots. Waterline length is typically lengthens as you heel, but in an m15 that is minimal given the short overhangs (now an old 6m is a different story); most boats will exceed slightly with enough power, especially with a flat run n wide stern like the motives have (supporting the boat even as the crest of the wave moves slightly aft of the stern)- so call that a max speed (except when surfing down a wave) of 5 knots. My mid 80s 2 hp gets my m15 to 4.6 knots or so at well under 1/2 throttle in calm conditions- any more and the efficiency drops as more throttle gets you less gain); the only time the little engine hasn’t done the trick was when I towed a broken down ski boat with a family of 5 in it off a lee shore and we tried to get them up lake to their trailer in 20+ knots wind and short 2’ seas (I ended up taking them to a more sheltered location downwind). My main issue in rough conditions has not been engine power; it has been keeping the prop fully submerged in short steep waves- something that got much easier when I cut the motor mount down 2”. I do still long for a replacement prop pitched to give more torque as you throttle up- I think that is one thing the electrics are doing well with their wide skinny bladed props to get full use of the engines power in slow speed applications- but the no doubt huge market for aftermarket props on a 2 hp built in 86 seems oddly underserved. Perhaps someone smart than me can set up a service to design and 3 d print affordable plastic props…. All in all I’ve been impressed by the m15 under power as long as I remember that she is a light, shallow draft boat that will never power into the waves like a full keeled heavy displacement boat (that would typically be far less lively to sail). Re autopilot power, perhaps one of the now common portable battery power supplies sold for campers- could even charge off outboard if you had the right set up, but still be able to run autopilot when outboard is off or at low power. Alex On Sat, Nov 6, 2021 at 3:49 AM Jim Sadler <jimsadler@jascopacific.com> wrote:
Any skippers know the hull speed of M15? My 2 hp will get the Pelican to 3.5 knts. To exceed hull speed would require that the vessel plane any exponentially more HP. That is my understanding Capt Jim
Get Outlook for iOS<https://aka.ms/o0ukef> ________________________________ From: casioqv <casioqv@usermail.com> Sent: Friday, November 5, 2021 7:24:51 PM To: For and about Montgomery Sailboats < montgomery_boats@mailman.xmission.com> Subject: M_Boats: Re: Outboard generator
Some small outboards can take an optional lighting coil or charge coil, it's an installable option on my 80s Yamaha 2hp. It produces a really small amount of current, designed to run nav lights, but might work with an autopilot depending on it's current needs.
Sincerely, Tyler
-----Original Message-----
From: Dave <scoobscobie@gmail.com> To: For <montgomery_boats@mailman.xmission.com> Date: Friday, 5 November 2021 9:35 AM PDT Subject: M_Boats: Re: Outboard generator
I'm not aware of any outboard that is of appropriate size for an M15 that has an alternator. Alternators usually found as option for motors 5HP or greater. Some 4HP motors have identical powerhead (aka block) as a 5 and 6 HP so an alternator can be added by the owner.
Also, the alternator doesn't start putting out any significant power until the motor is turning higher RPMs ... meaning the M15 is being overpowered (trying to climb the bow wave and dragging the transom deep in the water.
A M15 has absolutely no need for a motor greater than a Honda 2/2.3hp. larger motors are bad for boat trim, aka sailing ability, because of excessive weight hanging aft of the transom.
:: Dave Scobie :: M6'8" #650 :: Baba 30 #233 DEJA VU :: SV SWALLOW - sv-swallow.com :: former owner M17 #375 SWEET PEA - m17-375.com :: former owner M15 #288 SCRED - m15namedscred.wordpress.com <<-- new site!
On Thu, Nov 4, 2021, 11:32 PM Jim Sadler <jimsadler@jascopacific.com> wrote:
Looking for small OB that will power my tiller pilot Capt Jim M15
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