2000 2800SCR twin 4.3 Propeller question

[marcucho]

This is for people with SCR 2800 with twin carbureted engines and <b> 4 blades props </b>... What size and pitch are you using and how do they perform on the boat ?
Currently I have SS 18x17 on my boat with trim tap . To get on plane I need to hit at least 3500RPM and it does take some time, I am planning to install the swim platform and the dingy on it so more weight to the back of the boat is coming. I am thinking to get the 4 blades props which suppose to help to get out of the hole .. no much of a speeder here .. looking to get better gas LOL .. It is a boat :-) anyway and get on plane quicker... I still not used to get the engines on 4K rpm .. car owner mentality If I can keep the boat on plane at 2500 ~2800 RPm .. I am happy .. I forgot to add that I have bravo 2 configuration.

Thank Jose

[mmwjr]

Operating on plane under 3000 is not good for these engines and could cause damage. A boats engine is always under a heavy load on plane and pushing through water it’s like a car going up a steep incline with the entire family and luggage all the time.

[jparsons121]

Definitely discard the preconceptions from the ‘car owner mentality’. Two totally different applications. The 4.3s should be able to spin up to 44-4800 wide open throttle. If you can do this with your current prop setup that sets the baseline from where to start tweaking.
Don’t worry too much about where in the rpm curve you can maintain a plane..

Getting out of the hole quicker can be accomplished with a reduced pitch 3-blade or a smaller 4-blade. This reduces the load on the engines slowing them to spin up faster, but you if you go too small, the engine can over-rev and can exceed the WOT range.
You can play around with a number of variables using the mercury prop selector tool online.

WRT 3 vs 4 blade, the 4 blade will provide a bit more lift than a 3 blade. Based on cruising with some friends with a 2800, it’s not going to pop out of the hole like a ski boat regardless of the prop selection. Adding that weight to the stern may not be a good addition. They carried the dink on the bow as the weight on the stern had effects at cruise speed as well as getting on plane.

[marcucho]

Originally Posted by jparsons121

Definitely discard the preconceptions from the ‘car owner mentality’. Two totally different applications. The 4.3s should be able to spin up to 44-4800 wide open throttle. If you can do this with your current prop setup that sets the baseline from where to start tweaking.
Don’t worry too much about where in the rpm curve you can maintain a plane..

Getting out of the hole quicker can be accomplished with a reduced pitch 3-blade or a smaller 4-blade. This reduces the load on the engines slowing them to spin up faster, but you if you go too small, the engine can over-rev and can exceed the WOT range.
You can play around with a number of variables using the mercury prop selector tool online.

WRT 3 vs 4 blade, the 4 blade will provide a bit more lift than a 3 blade. Based on cruising with some friends with a 2800, it’s not going to pop out of the hole like a ski boat regardless of the prop selection. Adding that weight to the stern may not be a good addition. They carried the dink on the bow as the weight on the stern had effects at cruise speed as well as getting on plane.

Definitely I need to get out of my car owner mentality, , Having a wife and kids that they do not like to go "fast" 27 to 30 MPH hehehe . They just like to go cruising it is hard for me to actually push the engines on the 4K 4.5K rpm. So far I now that I can get the boat on plane when I hit the 3.5 K rpms then I can go down to 3.2 K rpm to keep it on plane until family complains that I am going to fast heheheh ..

I was looking for some information for the future in case I need to go into the 4 blades path, but first I have to try with the configuration I have and start from there

Thank you guys for the feedback .. now it is time to get my steering pin replace on my starboard outdrive.. but that is for another story
Thanks Jose