zodiac futura mark 3 15 feet top speed issues at altitude

[Travelertig]

Hello everyone I am new to the forum. Recently bought Zodiac futura mark 3 2005 with 60 HP Evinrude ETEC 2 stroke Got the boat to Lake Tahoe at 6,200 feet Unable to run faster than 23 mph-zodiac forums say 37-40 mph Also was unable to go over 4,000 RPM - zodiac says 5,700 Changed prop from pitch of 19 down to 13 Rpm get up to 6,000 full throttle but top speed only at 23 mile still Any advice

 

[Sea Rider]

Welcome to Iboats

High altitude affects all kinds of engines, least diessel ones. That Etec being electronically controlled should compensate better for high altitude effects + going to less pitch is what's normally recommended. 150-200 rpms is the usual numbers per pitch size difference. Was that sib top inflated ?

Were 6 K rpm achieved with new prop with just you alone on boat ? Which are the min-max wot rpm specs for that engine ? You can't pretend to achieve 100% combo performance at high altitudes as opposed to same one at sea level.

Happy Boating

 

[Chopperbill]

Went through the same ordeal this summer at 5000+ feet. I even went from 10 hp to 20 hp fuel injection. Still disappointing. Did get another prop but folded up the boat for AZ already. Will be at 300 feet and do some serious boating then. My dad told me of old stories at this altitude trying to pull skiers. Nothing has changed. Just have to deal with low hp. Problem with rubber boats is you can't just pile on more hp as the motor gets too heavy. You are also dealing with a boat that isn't easy to plane in the first place.

 

[ssobol]

Hello everyone I am new to the forum. Recently bought Zodiac futura mark 3 2005 with 60 HP Evinrude ETEC 2 stroke Got the boat to Lake Tahoe at 6,200 feet Unable to run faster than 23 mph-zodiac forums say 37-40 mph Also was unable to go over 4,000 RPM - zodiac says 5,700 Changed prop from pitch of 19 down to 13 Rpm get up to 6,000 full throttle but top speed only at 23 mile still Any advice

Going from sea level to 6200' altitude will cause a loss of about 20% of your engine's horsepower. With a lower pitch prop that gets you back to the proper WOT RPM range you are still going to have less speed because of the lower pitch (the prop does not move as much water per RPM as the higher pitch prop, i.e. less thrust). There is no way you can get the same speed from the same boat at WOT as altitude increases (speed decreases as altitude increases).

 

[Peter_C]

We had one of our dive club members take his larger E-Tec powered boat up there, and he could barely plane. Ran like a champ...at sea level. With the costs of bringing a boat to Tahoe it almost isn't worth it.

 

[Sea Rider]

We had one of our dive club members take his larger E-Tec powered boat up there, and he could barely plane. Ran like a champ...at sea level.

Gee, thought that Etec's compensated electronically better high altitude issues than standard carbed engines, going to higher altitude levels you will reach a point that no matter what you do, rejettting + playing with prop pitches, will achieve just fast displacements speeds, which is still much better than no boating at all. All engines are factory tuned at sea level, that's why they turn into being real pigs when working at high altitudes.

Happy Boating

 

[fbpooler]

There is less oxygen per measure of volume at higher altitudes, so an engine jetted for sea level runs rich and loses power. Remember that a proper fuel/oxygen mixture, compression and spark are required to develop power.

 

[Sea Rider]

Some old airplanes that use radial engines, have a compartment on wings to store oxygen, when flying over the high cordillera, oxygen is injected to each motor to compensate high altutude power loss and crosss safely the cordillera. Would be cool to inject through a small pipe small oxygen dosis direct into carb's throat and see what happens, definitely should compensate power loss.

Happy Boating

 

[Peter_C]

http://en.wikipedia.org/wiki/Nitrous_oxide
It is pretty easy to get and use. Cheap way to gain horse power, and would help at elevation.

 

[ssobol]

There is less oxygen per measure of volume at higher altitudes, so an engine jetted for sea level runs rich and loses power. Remember that a proper fuel/oxygen mixture, compression and spark are required to develop power.

However, if you adjusted the fuel mixture to be correct for the volume of O2 in the higher alt air (i.e. not running rich), the engine will still develop less power because there will be less fuel burned per stroke than at sea level. If you take an engine that gives X hp at sea level at max throttle, it will not be able to get that much HP at altitude no matter what you do to it (except supplemental O2). In airplanes some engines are derated at sea level in order to have enough margin to get the rated HP at altitude. Boat engines are not set up for this though.