But Thomas, a 21ft displacement hull shouldn't have a maximum hull speed much over 6 knots ( https://www.easycalculation.com/physics/classical-physics/hull-speed-calcula...). If you had an outgoing tide at 3 knots and were motoring against it at 4 knots, that is a speed of 7 knots relative to the water. Even if your outboard were 100HP, you wouldn't have gone much faster. Look at the resistance vs speed plot on this page http://forum.woodenboat.com/showthread.php?167599-Hull-speed-and-hull-effici..., resistance goes nearly vertical after you reach hull speed. I'm not sure if there are any studies on frequency of motor failures as a function of motor size, but my guess is that maintenance is a better predictor. Either way, I think waiting until the current was lower is the only non-daredevil thing to do in that situation. Sam On Mon, Apr 5, 2021 at 12:29 PM Thomas Buzzi <thomaspbuzzi@gmail.com> wrote:
I too have anguished about the tradeoff in power versus weight on the transom. With my present Monty 17 I have decided that a 3.5 tohatsu will suit my sailing needs. I do not plan on making it up to the San Juans as much as I would love to have a Monty up there. I am 74 and live in central Texas so lake sailing is my alternative. Once upon a time, I had a 21 foot sailboat with a 4hp outboard on it. I was attempting to motor into Port Everglades from the Atlantic Ocean on a falling tide. The outgoing current was over three knots, my diminutive ob could push me forward somewhat less than four knots. At this particular time of day rush hour traffic is heavy on the road which had a drawbridge over the entrance to Port Everglades. So there I was, full throttle, trying to enter the port against an outgoing tide. I was barely creeping forward under the raised drawbridge while making eye contact with the bridge operation attendant. He was NOT smiling as he peered down at me. He was holding up Friday afternoon rushhour traffic because of me and my tiny boat being pushed by a tiny motor. I thought I had cleared the bridge. It is HARD to tell where the top of your mast is and the bottom of bridges is from the cockpit. Suddenly the attendant started lowering the bridge! The onrushing steel sliced through the air about five feet aft of my mast. Just as suddenly I had the realization that if my suffering ob died at that moment I would be swept back under that bridge with all sorts of nasty consequences. I made it out of the funneled tide rush into calmer waters but learned that day that if there is any doubt about how much hp to get for your boat---there is NO doubt. Better to err on the side of caution (as in most everything in boating) that to suffer the daredevil's demise.
On Mon, Apr 5, 2021 at 2:07 PM Mark Dvorscak <mdvorscak56@gmail.com> wrote:
On my M23 there are definitely places in the San Juan Islands where I can barely make 0.2 kts head way against the current with a Honda 9.9 at full throttle (and other places where I would never even attempt to go against the current). Obviously there is a large difference between boats here, but a 2 hp motor on an M17 or even an M15 would probably have a similarly difficult time. Usually one can plan a course to coincide with the currents but occasionally you have the dilemma of choosing which location you will have to buck the current (or choose an alternate destination).
My 2¢ only. Others with M17 or M15 experience in the Islands may have better information.
Mark Dvorscak M23 M15 Former M17
On Mon, Apr 5, 2021, 11:35 Peter Zimowsky via montgomery_boats < montgomery_boats@mailman.xmission.com> wrote:
Hi all: I worry about the currents in the San Juan’s and the need for the 4 horse. But I will investigate getting smaller motor Pete
Sent from my iPhone
On Apr 5, 2021, at 08:18, Jon Barber <brbrbarber@gmail.com> wrote:
Why do you have a 75# outboard on a Monty 17? My 2 hp pushes my boat easily at 4kts, 1/2 throttle. Its plenty of motor. It weighs 27# and keeps the aft of the boat light and out or the water. The motor stays in the garage till I leave on a trip. When leaving I clamp it to the transom where it stays for the duration. To tow, I rotate the motor to the"reverse" position so it can't move up.
I launch many times in a season and not having to deal with the motor each time saves me a lot of trouble. I also changed to the Rudder Craft rudder with the extendable Mast support for the same reason. When I arrive at the marina the rudder is in place and I am also ready to raise my mast. Lately I have been rigging and unrigging after I launch. I find it safer to do so when the deck is not so high from the parking lot.
I also like no fuel tank in the cockpit. Nothing underfoot.
On a sail in the delta there was much water hyacinth tangling up on motors. Because my motor is mounted directly to to transom, the prop is closer and within reach to clear of obstructions.
Keep it simple!
Jon Barber Monty 17 Ol'44