Re: Trophy 1802 prop question
If you have the 19 pitch prop and you're getting too many revs at wide open throttle, you would need to get a prop with more pitch. For each 1" of increased pitch, you would loose roughly 200 revs at wide open throttle.
So, with your boat normally loaded, and in normal seas, try opening it up to maximum specified RPMs and see if you have more throttle left. If you have more throttle left, you would need to increase your pitch.
Sometimes with a fishing boat, this is not a good idea. For example, if you need to slow troll for Salmon or Trout, a prop with increased pitch may make your boat too fast at idle/trolling speed. I had this happen on my prior boat. The V8 engine was too powerful. I propped it up. I found that at my trolling idle, my boat was going 5 mph. I needed to be going 2.5.
Another aspect is the sea conditions. If you have lots of distance to go over smooth flat water, you would benefit from a speed prop. If you're crashing through the slop at moderate speeds, you might find that the lower pitch prop keeps the engine at it's sweet spot during "crashing through the slop speeds".
My dad actually has two props. A low one for torque. He uses this one for towing skiers and heavy loads. A speed prop when he's on the big smooth lake and he knows he'll be going some distance. This may be a good thing for your 1802. You may need one higher pitch prop when you're fishing alone. Add 3 Rhino sized fishing buddies, you may need to prop down and inch or two.
I typically will buy two or three props off ebay for approx $40 each and give them a try. I'll end up keeping the 2 that are really right and sell the ones that didn't work out. You'll be glad for that extra prop if you break a prop at a distant lake.
The only real risk you have is if you have too much pitch on a prop and are running wide open throttle at less that optimal RPMs (lugging the engine). You can damage an engine if it's struggling along at lower RPMs with a heavy load. This is particularly true with big diesel boats. You really need to have the engine turning at the right RPM at WOT.
With regards to fuel economy, the best instrument is the fuel flow meter. Either the smartcraft guages, a Lowrance LM200 or Floscan will give you gallons per hour. For example, on the boat pictured in the avatar, the engine has a definite sweet spot at 4200 rpms. I'm saving 5 gallons per hour. When the engine thermostat failed, the engine was running cold, I lost that sweet spot and burned a lot of extra fuel. I knew all of this due to the fuel flow meter on my dash. Another good thing about the fuel flow meter is keeping accurate track of the amount of fuel burned. On one trip, I new I need to run 45 miles. My tank had exactly 30 gals left. I knew at optimal cruising speed I was getting 1.4 mpg. With this info, I pulled into a marina and put in 20 gals to get me home. All of this was based on the info coming off the fuel flow meter.
Hope this helps.
