Why don't boats have more forward gears?

[bretto]

This may be a dumb question but why dont boats have more gears, at least 3. Logic seems to think that would help out on gas and not have the engine reving so high. Although I am relatively new to boating and can't say.
Brett

 

[SeaKaye12]

Re: Why don't boats have more forward gears?

Hi bretto,'

Yeah...it does seem sort of logical at first; doesn't it? But when you're running your boat; it's like a car going up a very steep hill all the time. Just cut off the power and notice how fast the thing slows to a stop...nothing like a car.

It takes a lot of power to keep a boat moving; unlike a car which has little comparable rolling resistance once it acheives a certain speed on level ground.

Marine engines are designed to produce that maximum power at high RPM's.....and would lug terribly if they were forced to run at lower RPM's (which could be obtained with the use of a different prop.)

Bad for the engine; terrible for performance. I think the closest we can come to more efficient "gearing" is through the more sophiscated props that are on the market today

I bet you'll get some very interesting responses from the techies here....I'll sit back now and await their replies.

Thanks for reading, Chuck

 

[bretto]

Re: Why don't boats have more forward gears?

Thanks Chuck

 

[DJ]

Re: Why don't boats have more forward gears?

Seakaye12 pretty much nailed it.

 

[swist]

Re: Why don't boats have more forward gears?

Large ships have enough inertia (if you cut the power they still go a ways, more like a car) that it does make sense to have a mechanism which decreases the effective gear ratio at higher speeds - but I believe thay do it with variable pitch props.

 

[tashasdaddy]

Re: Why don't boats have more forward gears?

back in the 50's my dad's buick was totaled. he took the engine and tranny out and mounted it in a boat. it was a automatic shift. unfortunately i don't remember much about the performance. as an 8 year old it would fly.

 

[Silvertip]

Re: Why don't boats have more forward gears?

If the Buick was a pre-1955 it had only one speed. It was a Dynaflow tranny. It did have a low range but it was not an automatically shifted tranny. Chevy PowerGlide (1950 - 1952) was another automatic with one forward gear plus low range. TurboGlide (1957 - 1961) was another one speed tranny although it used a multi-segment torque converter to provide CVT like power delivery. It did have a Grade Retard feature. (Not very useful in a boat). d

 

[DJ]

Re: Why don't boats have more forward gears?

Many ships do indeed use variable pitch props, just like airplanes.

That ability to vary the pitch is very expensive and requires some operator skill.

 

[Dhadley]

Re: Why don't boats have more forward gears?

There are 3 speed trannys for I/O's and inboards. The 2 main drawbacks -- space and $$$.

 

[Texasmark]

Re: Why don't boats have more forward gears?

I have an automatic transmission on my boat. It's called "prop slip". At "just on plane" I run about 35%. At WOT less (barely) than 10. By selecting the right prop and setup you can get your transmission......in some cases.

Mark