I think I need a prop coach

[Mwerks]

I have a 2008 Smokercraft 18 ft Pro-Mag with 150 Optimax. I have been following this site for awhile and there is a lot of good insight here.

I bought the boat with a 3 blade 19 pitch prop that ran up to WOT rpm but he boat ran at 4 mph or 47.2 GPS mpr well but porpoises a lot a mid range (25-30 mpr). I put a 4 blade 14.5 X 18 on it and it help ever so little. I put a hydrofoil on it and it solved all the issues and peaked at 5600 rpm and 41.7 mph.. It got up on plane fast and was steady at moderate speed. I was on a new lake in the Upper Peninsula and crashed the prop. The local Lund dealer only had a Spitfire 14 X 19 4 blade which handles mid range well but peaks at 5400 rpm and at 43.7 GPS MPH. I should add that the prop blows out any higher then 5400, The motor is rated for 5750 WOT but the dealer told me it would not be hard on the motor because I run at mid range often. I should add that I have a 9.9 pro kicker mounted and a 300 pound fishing buddy and a 22 gal live well in the rear. My motor seems too low from what I have read and should come up 2 holes with the foil on. I would like to get rid of the foil but can't tolerate the bouncing. I have two group 31 batteries mounted ahead of the helm and one group 27 in the rear. I need the magic prop. I was told smokers porpoise but the guy giving me the test ride ran it WOT on a small lake so it wasn't so noticeable then.

 

[82rude]

Putsmart tabs on her and dump the foil.They are by far a better option and work greathttp://nauticusinc.com/.

 

[Mwerks]

Smart tabs may be a better band aid but may be difficult to fit with the kicker in the way. This boat has the "hydra-lift" hull which I am told works somewhat like tabs. Has anyone fixed a Smokercraft with a prop selection?

 

[Texasmark]

First off my answer has to do with my experiences above 40 mph.

My experience with porpoising had to do with the AV plate being in the water when you were tuning the trim for the sweet spot. Porpoising normally is caused by either too high a trim angle or not enough speed......considering a boat with enough hp (like yours) for it to matter. Either tuck in the trim or speed up to stop it.

In running my boats of different kinds over the years up to 18' and 150 hp, pad boats, deep Vs, flat bottom, semi Vs, stepped type hulls, my best performance was to have the AV plate above the water when tuning the trim for best WOT mph and rpms. Usually this was accomplished by jacking up one notch off the transom ....move the bolt holes up one hole on the engine.

Getting the AV plate out of the water stops (for me anyway) the plowing action of the LU when tuning trim. It lets the boat float more, not forcing it's performance and allows you to better realize the benefits of the hull design. Think about it: If the leading edge of the AV plate is pointing at a downward slope, as is the case when tuning for max speed, it is essentially a plow forcing the stern of the boat down. This results in more wetted hull, lower rpms and top speed, and porpoising. So to stop the P, you tuck the trim in or speed up. Well sir if you are already at max throttle, only option is tuck it in and your speed and rpms suffer!

To wonder where you are on your prop selection, 150 on an 18' boat should put you up in the 50's easily on the right hull/load. With the load you are carrying, especially being transom heavy, probably not. However, once you setup your thrust properly, and get over 40, that weight doesn't matter all that much.

While we are at it, I liked to run ported props like the Laser II for a current edition excellent prop (just to name one of many). Ports let you run a high pitch prop on a stern heavy boat getting you both a good hole shot and good top end. Acts like 2 different props under the extremes of max load (hole shot) and max speed.

High rake (blades bent back) SS props of today are primarily bow lifting devices on their own (don't need trim to execute). In talking about bow lifting you are talking about above 40 mph where you are looking to get the hull up out of the water. Easy to see what I'm talking about. Just get up as fast as you can go and from that point, tuck the trim in a bit while watching your rpms and speed. What you experienced was the result of inadequate bow lift. Just think, if you could get more boat out of the water from your current max speed and rpms, you could go faster and realize your upper limit of your recommended rpm range. Lifting the engine and getting the AV plate above the water flowing past the LU at speed, helps in preventing the stern from plowing.

Tell you what. Here's an idea that will cost you nothing but time: Lift the engine 1 hole (up off the transom about ?"). Then for a number, set the AV plate parallel to the hull...just run a yardstick straight out from the hull and across the LU showing us/giving us the position of the plate vs hull bottom). Take it our and run it and tune your trim for the best performance. Come back with the results; how it feels to you, does it feel like it's lifting the hull as you are tuning the trim and the numbers, prop pitch, rpms, and GPS. The number or picture you give us is not where the AV plate will sit when you are running as 2 things cause it to be higher: Boat is not parallel to the water and water starts rising back up even with the surface as soon as the boat passes. But this is a starting point.

 

[jimmbo]

deleted

Tex beat me to it

 

[Texasmark]

deleted

Tex beat me to it

Thank you sir for the attaboy. Grin!

 

[Mwerks]

Texasmark,
your advice seem solid. I asked one of my buddies to help lift the motor and when he saw what was involved he ran away. I will try to find a lifting ring and go from there. This is a little more involved and may take some time.

 

[Texasmark]

Texasmark,
your advice seem solid. I asked one of my buddies to help lift the motor and when he saw what was involved he ran away. I will try to find a lifting ring and go from there. This is a little more involved and may take some time.

The lifting ring is the right idea. You can buy them, make them like I did, or rent one from a marine dealer (that rents stuff). What would be excellent would be an engine hoist, like you would use to pull an engine from an automobile. They are available for rent.

While you were away, I looked up today's version of your boat. If the boat is the same hull, no reason you can't move forward and get what you're after.