Since sailboats 'sometimes' really like to sail, 50 % surface area or less is the rule. Props with 5 or more blades are used for grabbing even more water and are common on tugs, w orkboats, ships, subs and can use 100% or more of the circle by using overlapping flukes. That means, when looking at your prop from astern, the sail prop covers half of the available area that water has to pass or grab, and power props grab 70% of it and also restricts water passage by 70% when sailing. Sailboat props are normally contain a surface of less than 50% of the overall area of the circle. Props are also designed with overall surface area integral to its intended use. You could make the engine scream, but the small prop would give poor boat acceleration and have little effect against headwinds or waves. To give a radical example, consider instead of your diesel engine, the manufacturer placed a 75 HP Outboard Engine on your boat(OK, even with an extended shaft). If you want to go fast with a planing hull, it is the opposite reduced diameter and increased pitch. Larger diameter props, are a design element of displacement boats bigger diameter/smaller pitch. Throw in some 1 or 2' waves will slow down any drive train combination, but these small waves, or larger, will have less effect on larger engines and larger diameter props.ĬSY didn't put a 24" prop on their boats because they liked to waste money. Flat calm reduces resistance to the hull and allows it to gain speed slowly over time to reach cruising speed. Doing 6 or 6.5 is easily doable and a whole lot less expensive.Ģ.
The ideal is to be able to get close to this 7.5 for a 44 in moderate conditions. The boat is trying to plane, bow up, stern down. The force required to move the boat through the water (and move the water up into the atmosphere causing a wake) is increasing radically the faster you go. Note that when motoring up to 5 or 6, the wake is minimal but when trying 7 or 8 the wake drastically increases. This gives the 44 a theoretical hull speed of about 7.5 knots. (1.26 used here is for fat boats like ours.a newer streamlined underbody would use 1.35 or there abouts)
To be able to cruise at hull speed, the engine needs to be able to run continuously at less than max and allow the boat to do 1.26 X the Square Root of the waterline length. Turbo choices will be debated for a long time to come.ħ-Drive train and performance includes engine, transmission ratios, propeller diameter as well as pitch.Ĩ-Changing engines is more than likely financially more costly and labor intensive, than rebuilding one or a direct replacement.ġ. Reading comments of others on Topica more than once and with care, sometimes catching the posts tagging along under the response, that have been sent outside of the mainstream Topica discussion, always proves interesting.ġ-Most folks would like to be able to cruise at or near hull speed.Ģ-Speed is not a constant and is subject to weather and wave conditions.ģ-Fuel consumption varies with engine size and amount of effort demanded from it.Ĥ-Some engines parts are getting hard to find for some engines but some are still serviced worldwide.ĥ-Yamaha's inboard is becoming a common choice.Ħ-Naturally Aspirated engines vs. I try to be fair, and keep to facts, but opinions mine and others will at times, disagree. It would take a very rare bird, to say that what they have, or what they have done, is 'not' what they now think is best, but in all conversation it does pay to listen or read carefully, so keep that in mind. sparks conversation and sometimes debate. Every year or so, a question regarding engines, transmissions, propellers, cruising speed etc.
0 kommentar(er)
