I bought a used boat a few years back, have always suspected that I am slightly under-powered or over-propped, but it has been "good enough" under most conditions, gets on plane reasonably well, cruising and top speeds are OK for me. Usage is mostly fishing (2-3 people), occasional family "cruises" (3-5 people), pulled a tube a few times (a little slow to get on plane while towing, but it always got up). Two weekends ago, I took my son and some in-laws (250 and 350lbs - plus gear, cooler, "snack" bag), had some trouble getting and staying on plane (it always planed, just struggled a bit - maybe a lot when the in-laws had to move to the stern because they couldn't handle the ?chop?). Everything was back to normal after we dropped off the two heavy-weights. For the last few weeks I have been doing research on-line, ended up here, ?lurking? (also did some testing / number crunching) - now am pretty sure that I am a bit over-propped, Christmas is coming, and I think it's time for a new prop.
I would like to: get on plane quicker when towing or with heavy load; stay on plane easier at lower speed / RPM's and reduce prop slippage to a more acceptable percentage (just learned about that). If possible, I would like to reduce a slight "slippage" (maybe ventilation?) issue in tight turns on plane and similar "slippage" under choppy conditions (not bad, I can control it by trimming in a bit in both cases). Not overly concerned about getting the absolute highest top speed, but would like to stay close to where I am at now.
Current prop: 3 blade painted aluminum stamped "Solas Myth D 3X13X19R", came with the boat (looked almost new then), now ?1/2" of paint worn off at tips, some small nicks in the tips, no major chips or dings.
Engine: 2006 Yamaha F115TXR outboard, good running condition, recently tuned, recommended WOT 5000-6000 RPM, max HP 115 at 5500 RPM, gear ratio 2.15, mounted directly to transom, anti-ventilation plate is 3" above keel (transom sets back 7? and rises 3? from back of keel), has a Sting-Ray Hydrofoil mounted to the plate (tried removing it once - from memory: doubled my time to plane; increased bow-lift a little; no significant change in speed or RPM - I put it back on), the foil does have a small chip on the rear corner.
Hull: 2007 Cape Craft 19CC Bay (hull is clean but could use polishing), fiberglass (encapsulated wood stringers & transom), 150 max HP, capacity 7 people / 1275 lbs, length 19', beam 7'11", modified V (9? dead-rise), no trim tabs, hull weight listed as 1725 lbs - plus lots of extra weight: 40 gal gas tank; 24v trolling motor plus batteries; additional deep-cycle battery (for lights, Sonar/GPS, VHF, live-well pump when not under power); on-board charger; anchor and standard safety equipment.
Usage: 85% fishing (or going to), 15% cruising/tubing - 25% salt, 50% brackish, 25% fresh - at sea level - generally 2-3, rarely 4+ people.
Current performance with average load - 3 people (?420 lbs), ?30 lbs extra gear/food/drinks, ?8 gallons gas:
WOT @ 5500 RPM - 36 MPH (22% slip) (I rarely run at WOT); fast cruise at 5000 RPM - 33 MPH (21% slip); comfortable cruise - 4500 RPM - 31 MPH (19% slip).
Also did a light load WOT test (just me with ?5 gallons gas) - not much difference, maxed at 5550 RPM - 38 MPH.
Slip numbers seemed high, so I checked tach vs an inductive clip on tach, same ?50RPM from idle to about 3500 (was afraid to go higher without a load on engine).
Went to a local marine dealer (had a few props in stock, not sure how "expert" he is), he advised that going to same size stainless 3-blade prop with exhaust vent holes (he recommended a Turning Point Express) would probably be about the best I could do prop-wise, or lose the hydrofoil and add trim tabs (too expensive for my taste). He said that ideal WOT RPM was 5500 since that is when peak HP is generated. While I agree about going to stainless, as much for durability as for the slight performance boost (actually, most of what I read says an efficiency boost, does this relate to slip? - don't see how?), I'm not sure about his other opinions. After my research, I am considering a Solas Titan HR 4-blade stainless 13x17 (3453-130-17) instead. My reasoning:
Al to SS: +50 RPM plus slightly better all-around performance/efficiency plus better durability;
19 to 17 pitch: +400 RPM plus better hole-shot, plus hopefully reduce overall slippage;
3 to 4 blade: -100 RPM but better hole-shot, stay on plane at lower speed, reduce slippage in turns and chop (and hopefully overall), but will add more drag/lose some speed.
If I got the math and numbers right, at my average load, I think I should end up around 5850 RPM at WOT (still within range, give me a little leeway for light loads) - even at 22% slip, I think I would make around 33-34 MPH. I can live with losing 2-3 MPH that I never really use if I can improve hole-shot. Hopefully I will decrease slip (even improving to 18% slip should give me about the same WOT speed).
Additional questions thought up while researching:
Is cruising for extended periods below 5000 RPM OK or is that considered "lugging" the engine (should I consider dropping to a 15? and watching my RPM?s more carefully - I don?t tend to be a tach watcher, drive more by the way things feel)?
Other than being able to replace just the hub or prop, and the cost, are there any advantages / disadvantages to the two piece hub/prop systems?
If my thinking is out of whack, or if you have other suggestions, please let me know, I'd rather be called ignorant (I admit to being a NOOB at this) than get it wrong. Thanks in advance, sorry this ended up so long.
I would like to: get on plane quicker when towing or with heavy load; stay on plane easier at lower speed / RPM's and reduce prop slippage to a more acceptable percentage (just learned about that). If possible, I would like to reduce a slight "slippage" (maybe ventilation?) issue in tight turns on plane and similar "slippage" under choppy conditions (not bad, I can control it by trimming in a bit in both cases). Not overly concerned about getting the absolute highest top speed, but would like to stay close to where I am at now.
Current prop: 3 blade painted aluminum stamped "Solas Myth D 3X13X19R", came with the boat (looked almost new then), now ?1/2" of paint worn off at tips, some small nicks in the tips, no major chips or dings.
Engine: 2006 Yamaha F115TXR outboard, good running condition, recently tuned, recommended WOT 5000-6000 RPM, max HP 115 at 5500 RPM, gear ratio 2.15, mounted directly to transom, anti-ventilation plate is 3" above keel (transom sets back 7? and rises 3? from back of keel), has a Sting-Ray Hydrofoil mounted to the plate (tried removing it once - from memory: doubled my time to plane; increased bow-lift a little; no significant change in speed or RPM - I put it back on), the foil does have a small chip on the rear corner.
Hull: 2007 Cape Craft 19CC Bay (hull is clean but could use polishing), fiberglass (encapsulated wood stringers & transom), 150 max HP, capacity 7 people / 1275 lbs, length 19', beam 7'11", modified V (9? dead-rise), no trim tabs, hull weight listed as 1725 lbs - plus lots of extra weight: 40 gal gas tank; 24v trolling motor plus batteries; additional deep-cycle battery (for lights, Sonar/GPS, VHF, live-well pump when not under power); on-board charger; anchor and standard safety equipment.
Usage: 85% fishing (or going to), 15% cruising/tubing - 25% salt, 50% brackish, 25% fresh - at sea level - generally 2-3, rarely 4+ people.
Current performance with average load - 3 people (?420 lbs), ?30 lbs extra gear/food/drinks, ?8 gallons gas:
WOT @ 5500 RPM - 36 MPH (22% slip) (I rarely run at WOT); fast cruise at 5000 RPM - 33 MPH (21% slip); comfortable cruise - 4500 RPM - 31 MPH (19% slip).
Also did a light load WOT test (just me with ?5 gallons gas) - not much difference, maxed at 5550 RPM - 38 MPH.
Slip numbers seemed high, so I checked tach vs an inductive clip on tach, same ?50RPM from idle to about 3500 (was afraid to go higher without a load on engine).
Went to a local marine dealer (had a few props in stock, not sure how "expert" he is), he advised that going to same size stainless 3-blade prop with exhaust vent holes (he recommended a Turning Point Express) would probably be about the best I could do prop-wise, or lose the hydrofoil and add trim tabs (too expensive for my taste). He said that ideal WOT RPM was 5500 since that is when peak HP is generated. While I agree about going to stainless, as much for durability as for the slight performance boost (actually, most of what I read says an efficiency boost, does this relate to slip? - don't see how?), I'm not sure about his other opinions. After my research, I am considering a Solas Titan HR 4-blade stainless 13x17 (3453-130-17) instead. My reasoning:
Al to SS: +50 RPM plus slightly better all-around performance/efficiency plus better durability;
19 to 17 pitch: +400 RPM plus better hole-shot, plus hopefully reduce overall slippage;
3 to 4 blade: -100 RPM but better hole-shot, stay on plane at lower speed, reduce slippage in turns and chop (and hopefully overall), but will add more drag/lose some speed.
If I got the math and numbers right, at my average load, I think I should end up around 5850 RPM at WOT (still within range, give me a little leeway for light loads) - even at 22% slip, I think I would make around 33-34 MPH. I can live with losing 2-3 MPH that I never really use if I can improve hole-shot. Hopefully I will decrease slip (even improving to 18% slip should give me about the same WOT speed).
Additional questions thought up while researching:
Is cruising for extended periods below 5000 RPM OK or is that considered "lugging" the engine (should I consider dropping to a 15? and watching my RPM?s more carefully - I don?t tend to be a tach watcher, drive more by the way things feel)?
Other than being able to replace just the hub or prop, and the cost, are there any advantages / disadvantages to the two piece hub/prop systems?
If my thinking is out of whack, or if you have other suggestions, please let me know, I'd rather be called ignorant (I admit to being a NOOB at this) than get it wrong. Thanks in advance, sorry this ended up so long.
