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Everyone here has a dilemma. Here's mine??
History....Formula 292 Fasteck. I have always had a problem with prop slip. I removed the Bravo 1's 28P 4 blade props and installed BBlade's 4 speeds. Both sets of props where not Labbed. The boat gained some mph and reduced prop slip with the BB. Although I feel the slip is still high (upper teens).
I removed about 300 lbs of exhaust manifold weight by removing cast iron and adding aluminum/SS. So the stern is that much lighter. I also added about 100 lbs to the cabin area. I am not carrying 19 gallons of potable water in the V-birth. Problem??.... The boat at present cruises more efficiently at 3400 rpm at 42 mph consuming 22 gallons of gas per hr. Prop slip is 17%. BUT the drives have to be all the way in and the tabs all the way up. ANY deviation from that will reduce speed. If I increase speed then I can adjust the drives out and tabs down for the best top end of the rpm range. The degree of adjustment is determined by speed. I have my own opinion but am holding back so not to influence yours... Thank you for your time. |
Removed 300 from stern, added 100 forward of amidship
Best cruise with drives tucked in and tabs up Will guess if drives come out at best cruise, the boat starts to porpoise? What happens when you fill the water tank? Tabs down with drives out and best speed, you need more weight forward. |
Yes, when drives come out at best cruise, the boat starts to porpoise. But before it porpoises, the speed decreases by 6-7 mph. I always run with a full tank of gas. That weighs over 700 lbs. I don't really want to carry around extra weight.
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My boat does fine until a bunch of friends show up. I'll have 8 folks (some large) and I have to tuck the drives in and keep them there to keep from porpoising. When there is just the 2 of us, then no issues.
Thought about something else, you have 28P 4 blade props, that is creating a lot of lift for a 7K lb boat. Are you reaching 5K RPM's at WOT? |
I am running 26P Bblades. And yes 5K WOT
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If this isn't a new to you boat (not original owner), then wonder how the drive vent plate lines up with the bottom of the hull
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On both drives, The outer edge of the inboard anti ventilation plate is 3 1/4" above the top of the setback. Top of the setback to the deadrise is another 1 1/4" The outer edge of the outboard anti ventilation plate is 1" above the deadrise.
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Not sure why you are so hung up on slip percentages. Higher slip is not a horrible thing and is pretty normal on 292 Fastec's.
Higher slip %'s actually stress outdrives less. What exactly is the dilemma other than you have to have trim and tab set a certain way to be most efficient. You are getting almost 2mpg at cruise speed. |
Propeller slip is thrust wasted. I don't do hole shots, wave jump, race or run WOT every single time I'm out. I ease up on plane. If I was to get lets say, 10% slip, that would equate to an additional 4 mph or a saving of 20 gallons of gas when filling up. Projected numbers..
I may run better now with the drives all the way in at 3400 rpm. I may run better if I could tuck in the drives more, but I can't. With the drives tucked in, most of the thrust is trying to keep the bow down instead of moving forward. If the stern was higher in the water and the ability to move the drives out where the propeller centers where parallel to the keel, all the thrust would be forward. Then I would have full range to adjust the outdrives to suit the conditions and efficiency. So what are your recommendations to helping me with my dilemma? |
Drive spacers or 5 blades would probably help...maybe talk to brett at bblades...he can I'm sure lab your props and help this situation...have the drives been off recently? is this a new condition that just started or has it always performed this way?
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There is a 2002 boat test which list its best cruise at 3400 rpm at 34.4 and getting 2.12 mpg, and top speed at 70 mph
https://www.boattest.com/oem/386/boats/138/0/ Another 2015 but obtained numbers from Formula showing with 350mag getting 62 to 65 mph and 377 with 3 mph increase. Best cruise at 4000 rpm and getting 49 mph. Also noted if it had 8.2 motors the balance would be thrown off https://www.boattest.com/review/form...41_292-fastech On Formula forum there is a 312 and 292 with porpoise issue and member fossil fuel mentioned to have the props turn out instead of in to help 2 Fastech Questions... Extension boxes? Ladder? Anyone got a 311 that doesn't porpoise??? |
hows the bottom of the hull?????
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BB.... I was thinking the same thing. Drive spacers, five blades. Along with a longer tube diffuser ring or extension boxes. The latter being the last resort.
Dodge..... Thanks for the links. The closest was the 2015 review. But there figures make best light of the boat. For instance, the 7000 lbs weight to HP ratio is false. The 7000 lbs is dry weight. Plus Formula changed to a 97 gallon gas tank removing the 113 which I have. Finally the boat looks like it came of the show room floor. So the bottom looks like a new born baby's ass... |
I think he was saying like is there a hook in the bottom rather than if it's clean..from what I've read I believe a hook can and will cause these issues
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Originally Posted by AmiableDave
(Post 4682350)
Propeller slip is thrust wasted. I don't do hole shots, wave jump, race or run WOT every single time I'm out. I ease up on plane. If I was to get lets say, 10% slip, that would equate to an additional 4 mph or a saving of 20 gallons of gas when filling up. Projected numbers..
Look at it this way.....Which one is better??? Assume they have the same cruise rpms and speed and handle equally well Prop 1 runs 72mph at 5000rpms with 22% slip Prop 2 runs 68mph at 5000rpms with 12% slip Which one is better??? |
I'd call Brett. BB can tweak the props to give you more stern lift. Not sure if they have a diffuser ring on them or not, but a diffuser ring will also give you more stern lift. But that doesn't mean your props will be more efficient, it just means you will get more stern lift and possibly be able to trim out a little at cruise. It is pretty common that if you over trim your prop slip increases. Obviously your current set up doesn't like much if any trim at 40mph. That's not necessarily a bad thing. What is your slip across other RPM readings.
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Griff, Your last makes sense. I just know the boat can be set up better. Its the how, with out spending a small fortune that's got me scratching my head. Don't get me wrong. I don't mind spending money if it ends in success.
Mentalpause, Brett will be called at a later date. There is a wealth of knowledge here. If someone comes up with a worthy idea that I can do, I'll do it first. With WOT 5000rpm, the slip goes to 13%. But twin stepped hulls are most efficient at high speeds. |
I know you don't want to carry the extra weight, but have you ever filled the water tank and tried a run?
If not maybe ask the wife if she would go to the bow to see what happens, do note that if wife goes to the bow, its more in the bow and less amidshipsgallons The 19 extra gallons of gas 114 pounds |
Originally Posted by AmiableDave
(Post 4682235)
Yes, when drives come out at best cruise, the boat starts to porpoise. But before it porpoises, the speed decreases by 6-7 mph. I always run with a full tank of gas. That weighs over 700 lbs. I don't really want to carry around extra weight.
That amount of fuel is not helping your slip numbers at all. That much fuel will also change the running attitude of the boat. My boat is night and day different with full tanks and 1/2 tanks. Your slip numbers really are pretty normal at 17% at cruise and 13% at WOT. You might be able to get them down a couple % with some prop tweaking. Although you have a stepped hull, Fastech's are still not extremely efficient and the 292 had its quirks with needing the 1.65 drives to run best and being somewhat slow to get on plane. |
Yeah I'm not sure why you always run with a full tank. My last boat was night and day difference running at 1/2 tank vs. full. Felt like a completely different hull and that I gained 100 HP.
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Originally Posted by Griff
(Post 4682526)
It doesn't really work that way. Slip is not wasted thrust. It really doesn't take hardly any hp to spin the prop if its slipping. If you reduce your slip, most likely your rpms will go down when the same amount of throttle is applied.......which is not the same as running at the same rpms. You are thinking that reducing slip is linear with speed and by reducing slip, it will automatically increase speed by the same percentage. If you decrease slip, it will create more load and reduce rpms.
Look at it this way.....Which one is better??? Assume they have the same cruise rpms and speed and handle equally well Prop 1 runs 72mph at 5000rpms with 22% slip Prop 2 runs 68mph at 5000rpms with 12% slip Which one is better??? Bottom line is wrong prop for the particular application can account for poor slip numbers but also hull/drive setup can impact slip numbers. I believe you have a setup issue if you can only run around with the drives all the way down. |
Originally Posted by Trash
(Post 4683251)
And to add to what Griff said, if the boat were tied to shore and put it gear prop slip would be 100% all the time. So slip is not always about the prop, but can also be how hard the hull is working against the prop (i.e. hull drag is high).
Bottom line is wrong prop for the particular application can account for poor slip numbers but also hull/drive setup can impact slip numbers. I believe you have a setup issue if you can only run around with the drives all the way down. |
No, I don't have any pics of the boat running at cruising speed or at any speed. The Bravo 1, 28 pitch props that came with the boat SUCKED. Some Formula owners swear by them. I don't. I increased the Diameter of my props to15 1/2" and decreased the pitch to 26P. That Increased my speed by 5MPH and decreased the slip, in some areas by half. About the fuel. I keep the gas tank full because, (1) Condensation. I'm in Florida.. It's HOT. It's Humid. Enough said. (2) Out of the 113 gallons I carry, I may burn 1/2 in an outing. (3) Practicality. Once on the water, I'm not going to cut short my enjoyment because I have to stop what I'm doing to put damn gas in the boat. (4) Safety. I'm also not going to run out of gas when the going gets good. Or if I want to extend the day. NOW for you late comers saying your boat with 1/2 a tank of gas compared to a full tank is, Night and Day. WELL mine is night and day now with the removal of 300 lbs of cast Iron ( That's about a 1/2 tank in weight) and different props. The boat Jumps up on plane now along with the improvements mentioned above. And I'm still carrying a full tank of gas. And Trash, You forgot to say that if I left my boat home, I'd have 0% slip. SO again, how can I get the drives out with out losing speed. How would drive spacers effect the geometry? |
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