3 to 4 blade Prop - '81 SeaRay SRV 207

[blamtro]

Boat is a 1981 SeaRay SRV 207 (20 ft) with MCM 260 Horsepower Chevy 5.7 V8, Alpha drive. I previously ran an aluminum Michigan Wheel Vortex 3 blade 14.5 x 19, would top out at 4600 rpm, dont know speed.

Looking to go to 4 blade for more holeshot, not concerned with top speed but want it proped correctly as others may drive the boat and I dont want the option to over rev it.

Purchased a Michigan Wheel Appollo 4 blade stainless 14 3/8 x 18. Did I get the right prop? Its not returnable if I use it. If not, recommendations? The prop calculators out there have limited info because of the age of the boat.

 

[CraigBarnard]

I have had zero luck with 4 blades.
Might be due to the fact i have listened to these so called "proffessionals" in the marine industry.
They all seem to push 4 blades but i have always gone back to a 3 blade.
Everything i have researched shows that the less blades the best performance.
However that just my 2 cents worth.

 

[batman99]

For my outboards (previous Force 120 and swapped in Johnson 115) on 16.5ft Bayliner Capri, my boat likes 4-blades much better than factory 3 blades. For my OMC (Johnson), I use Amita-4 15' for heavy loads / tubing and Amita-4 17' for long distance cruising. both are aluminum props. For my boat's unique design characteristics, 4-blade is better hole shot, better stern lift and better in "R" gear at dock area as well. Your inboard may like 4-blades better than 3-blades. Not too sure. It all depends on each unique boat and one's driving conditions.

For more details, surf: https://www.precisionpropeller.ca/3-blade-vs-4-blade

 

[Scott06]

For how you want to use it you made the right choice. My experince was based on 4 blade vortex use, assume the Apollo would give similar results. If you're worried about it return the Apollo and get a 4 blade vortex for half the money.

I would expect you will loose 100-200 rpm at WOT but I wouldn't go down more in pitch, you're right on the money there

 

[blamtro]

Update: I bit the bullet and installed it. I ended up at 43 mph gps, 4250 rpm @ WOT.

 

[batman99]

Found "WOT...Wide Open Throttle...then it should be between 4200-4800rpm... cruising is around 3600-3800 " on a different boating forum. Sounds like your new 4-blade is within acceptable WOT range.

 

[Sea Rider]

Update: I bit the bullet and installed it. I ended up at 43 mph gps, 4250 rpm @ WOT.

Was WOT rpm achieved while lightly, medium or fully loaded ? Don't know why boaters swears with 4 blade props when traditional 3 blade ones performs excellent, just need the right pitch. Anyway with just 4250 WOT revs you're at the extreme lugging side which is no bueno for that engine..Just for the record, post your load while testing..

Happy Boating

 

[H20Rat]

Was WOT rpm achieved while lightly, medium or fully loaded ? Don't know why boaters swears with 4 blade props when traditional 3 blade ones performs excellent, just need the right pitch.

Pitch is only part of the story. I tried numerous 3 blades, my planing speed was always 20 mph (or higher). With a 4 blade I can get down to a stable plane at 17 mph, 15.5 to 16 if I don't have much fuel in the tank. Dropped a couple mph on the top end, which I couldn't care less about. Holeshot seems slightly better but I don't have any qualitative numbers to back it up. Vibration is less (well, non-existent), but that could have been due to a nick on the 3 blade. Technically any rotating prop assembly can be balanaced, no matter the blade count.

 

[blamtro]

I was loaded nearly full tank of fuel (~35 of 40 gal), 1 60# dog, 2 toddlers, 4 adults, and 1 cooler full of ice, lunch, and drinks. Pretty typical for how we boat.

SeaRider, are suggesting I go the other direction in pitch? To 20"?

Update: I bit the bullet and installed it. I ended up at 43 mph gps, 4250 rpm @ WOT.

 

[redmen62]

You're pretty good and loaded... If you were to do some WOT runs with just you and the dog, You'd at least be closer to the middle and i'd be closer top of the range

 

[Sea Rider]

One question you have to ask yourself, will "always" go boating loaded as described while running at wot ? seems it's a family leisure combo. If wanting to get the max HP out of that engine, dial a prop that runs at full wot rpm range.The current in use while highly loaded is lugging the engine. Bear in mind that when correctly proped to run heavily loaded, when lightly loaded, engine will over rev badly, watch tach.

What's your current 4 blade prop while running 4250 wot rpm ? Boat model, HP and load is a unique world, and it's specific for each personal type of boating.

Happy Boating

 

[blamtro]

More info, had some more time to go test and swap props while on the water so all these numbers were taken within 20 mins of each other. 85 and sunny out, little to no wind, no chop, only ripples, all MPH # are gps. Drive was trimmed to the same setting according gauge, probably 75% of all the way in. Used that position for both prop tests. Although it was just me and 1/2 tank of fuel, I would expect these numbers to have a greater difference in favor of the 4 blade when 4-6 adults + cooler is on board.


WOT: 45mph @ 4350rpm with 4 blade. Plain in 5 seconds @23 mph. Michigan Wheel Appollo 4 blade stainless 14 3/8 x 18. #993204
44mph @ 4500rpm with 3 blade. Plain in 7 seconds @ 25 mph. Michigan Wheel Vortex 3 blade 14.5 x 19 Aluminum. #992004

Both props are in perfect condition with no dents, dings, ect. Both using the XHS hub system.

Plaining numbers were taken with average of 3 passes each time idling in forward gear to slam forward throttle.

I was shocked that the 4 blade was faster out of the hole and on the top end.

 

[Sea Rider]

Have you tried trimming for boat and anticav plate to ride parallel to water level when on plane, try at least one run on same water cond and check if differs from running while trimmed as posted.

Testing props while lightly loaded it's a differente story than when heavily loaded. All those posted number should fall into the deep blue once boating with 4-6 upn and extra load. 4350 and 4500 wot rpm are still off from ideal 4800 if that's the max wot rpm range stated for that engine.

Run a test with say 4- 6 up and usual extra load with best prop you condider best from posted 2 and report wot rpm.

Happy Boating

 

[blamtro]

The Max WOT rpm range of this motor is specified at 4200-4600.

43 mph gps, 4250 rpm @ WOT from the original test using the 4 blade stainless, I was loaded nearly full tank of fuel (~35 of 40 gal), 1 60# dog, 2 toddlers, 4 adults, and 1 cooler full of ice, lunch, and drinks. Pretty typical for how we boat.

 

[Sea Rider]

Just + 50 wot revs over the lugging zone of 4200 wot rpm. Need to drop at least one less pitch to pull wot revs higher towards max wot range as currently loaded. Other alternative, send tested prop to a prop shop and have it repitched at least one less in pitch. Will work much better than current one.

Happy Boating

 

[blamtro]

So you are suggesting to drop to the 14-5/8x16?

Rule of thumb is 200rpm gain for each inch in pitch drop?

This would put me at 4650rpm?

https://www.miwheel.com/outboard-pro.../recreational/

List of 4 blade apollo props available:

993203 (RH) - 14-5/8" x 16"
993213 (LH) - 14-5/8" x 16"
993204 (RH) - 14-3/8" x 18"
993214 (LH) - 14-3/8" x 18"
993205 (RH) - 14-1/8" x 20"
993215 (LH) - 14-1/8" x 20"
993206 (RH) - 14" x 22"
993216 (LH) - 14" x 22"

 

[Sea Rider]

So 43 mph gps, 4250 rpm @ WOT was achieved using the 4 blade 18 stainless prop as usually loaded, right ? To be honest can't recommend how much pitch you need to drop if plan counting with 4 blade props. Could be just one or 2 less in pitch to rev at the sweet 4600 max wot revs.

The rule of thumb that states -200 wot revs per pitch reduction in most cases does not work, have only seen that reduction on very heavy working boats, much heavier than recreational ones. How about repitching same 18 prop to a 17 and check how much wot rpm OB gains with just one lesss pitch. This is the least costly investment than going straight for a 4 blade SS 16 pitch and...

Happy Boating