Thanks Knot, nice read. Sure could use a bit more real world numbers by changing over. I will time my props for next season, maybe this if I get the urge again. Keeping my eyes open for the 25 XR now. Kind of makes me think, I have a good 20% prop slip now, if the 25 reduces it down to 15% or a bit lower I may need 24's. Don't know

I just can't believe your slip is so high. If you did not modify your stock drive height, I wonder if something is up with your current props. I know that out of the box, standard 3 x 3 prop sets are notoriously out of balance and can have variances in pitch across the blades.

Depending on what calculator I run, I am between 8 - 10% slip.

sorry somehow I deleted instead of edited
Ive been dealing with a similar challenge on my fat pig and have read a ton. Some publications say that 20% on a cruiser hull is normal at top speed and performance hulls interrupt the water less and shouldn't be used as a comparable for prop slip. This may also contribute to the lack of top speed increase that AllDodge and I both saw after our re-power. I also think I am calculating wrong, most of us are trimming up for that last mph then using those numbers to calculate slip but if I trim down slightly I may lose 200 rpm and only 1 or 2 mph, as a result my slip numbers can improve significantly. Then there is the weight and fuel load that most cruisers are carrying during the tests. At the end of the summer I am going to run a quarter tank and empty my crap drop my bimini and do a true run in both directions documenting speed and rpm at 1000 rpm intervals and I bet my numbers become much more normal "for a cruiser" I suspect the same thing would happen with Al Dodge. Then again what do I know? lol

I have calculated at 3600 thru 5050 rpm and for the most part it stays about the same amount of slip. Been using bblades calculator to get the numbers. Went out this after noon and checked the prop timing, While it doesn't appear I'm dead on maybe one tooth off. Something I'm going to check out when I pull the boat out this season is the height or the XR upper. As before I have my original B3 lower but a new XR upper. Don't know if the height of the XR is the same height as the standard B3 upper.

The boat is lighter in the stern from the water soaked foam and I it is real touchy with the trim, takes next to nothing to start proposing at 3600 rom and above. Anything from 4500 to WOT it not so much an issue with the trim. This is also having tabs all the way up. If I put the tabs down to take off it takes a bit longer. With the previous power I had to have the tabs down to get up

AllDodge, since our talk I pulled the trigger to work at getting mine dialed in a little better. I have some news, but I am still in the testing stages. I spoke with Chad Hill in regards to his Signature 4 x 4 wheels and decided to order a set. I bolted them on and put some hours on the boat this weekend, but the bay was snotty and couldn't get some WOT runs. I did get rid of the slip getting on plane, in fact its impressive getting on plane using the same pitch as i had with the Merc 4x3s. I also can get into aggressive turns like I use to with my B2 before the repower. The boats overall behavior was drastically improved also. I was running in a 3' chop and it let me be able to trim on top and stay steady without porpoising issues. I am working with Chad of what is the next step. He offers an exchange service in which I send these back and either tune them or send me another pair to get really dialed in. I almost feel with his wheels I can go up to 26 pitch which should give me a boost in speed and get me right where I want to be with still improving how it pushes on plane compared to the 4x3s I was running for a while.

I can keep you posted, but I would really consider this an option. Tell him Tom from Formula Owners of New Jersey directed you his way too.

Check out the full resto of It Don't Come Easy here..... http://www.formulaboatsforum.com/VBF...y-Formula-26PC

Still doing research on which way. Going done to the dock later to measure another boat on a lift which has XR's. Something just doesn't add up and need to figure out what is happening. Wouldn't mind trying the 4x4 or the 4x3 but need to find out what is different. Was thinking of putting my 3x3 24's back on just to see if the boat cruises like before. I use to run 3600-3800 doing as I remember correctly 34 to 35mph, which puts me in the 14 to 17 slip area. Now I'm turning the same rpm doing about the same speed so my slip is high, just something is off.

Did look at your build, very, very nice work, cudo's and nice family

I havn't been on the Formula forum for a while since the last weird happing on a thread with GENSET. Still don't get it but oh well, plenty other things here and on iboats

I would give the 4x4s a shot. With my luck of actually buying something that works, I admit I was skeptical but needed to do something because I just wasn't satisfied yet. I know there is some left. Most people would hop on my boat and be ecstatic but I just know there could be something left on the table so I am going to give it one last shot dialing her in.

Your HP and TQ may be located at different RPM levels with the new build which will throw your comparisons to the previous setup off. Ultimately you really need to get her to grip, with that much hp you should net some good results speed wise once you do.

Thanks for the kind words, this is why I hopped on here because I can appreciate what you are trying to do.

Ah i just had to look back and see what you were referring to and I see that. Hey it's silly Forums, lots of different views. I bumped into a few posts through in this thread that were questionable but.... like i said it is Forums, kinda part of the game here. For what negatives you will come across you will get your positives.

No issue with someone saying something that upset me enough to not come back. Don't really remember what it was all about but it came down to I explained my reasoning behind comment. The moderator simply gave a comment which resembled something like (I don't have to explain why) and then closed the thread, wasn't even my thread. So figured if the guy running the show gets that way maybe I should stay away. I still pop in every once in a while

A 4x4 or 4x3, I'll try one and bblades is showing a set of XR's for 720 I think

Hmmm your work is so thorough i almost hate to say this but i must pee in the punch bowl so to speak.You need clean your hull bottom up ....strip the paint the amount of drag it's creating is huge and if you go there it would be wise to see or look for hook...When you trim and she's bouncing or falling off is drag more than probably....now i know how much work that is but it's highly suspect......:party-smiley-004:

Not worried about peeing in the punch, appreciate the comments. While the boat bottom does have a hook the bottom while not smooth its pretty clean. Don't see how bottom paint has much of an impact on a cruiser doing 35mph.

It could be as simple as the 26 pitch I'm currently using have a problem which was not found with the eye ball. I could put the 24 back on and it should run like it use at the same rpm. Old 24 turning 3600 rpm doing about the same speed as the 26 do now.

Did find out that the XR upper is the same height as the standard bravo, so prop is still at same height as before

Bottom paint can cost a boat as much as 10mph and more and you have a lot of hull and weight in the game there. I am sure more will chime in on this area If it drags at 50mph the drag will be greater at 35...read wetted surface area.

Ok I'll agree bottom paint causes drag. My current issue is I use to run 45 at WOT and 35 MPH around 3600 or so rpm with 24 pitch props and 415hp. I now run basically the same numbers with 26 pitch props and 530hp or so. My bottom is painted the same as it was before the repower. I have more prop slip

Do i have this right your gearing in both cases was 2.0....not 1.65 and your mixing lower's the original lower was?? and the lower your using now...Yes i would imagine your a bit twisted right now. the hull drag (paint has remained the same the only constant...

The ratio remain the same. Was told I needed a 1.65 drive but that was a bust, the boat wouldn't even come out of the water. So I removed the new 1.65 and installed my original 2.0 lower, but changed from 24 to 26 props. Hull has remained the constant.

Trying to put this together in one spot

Before 46mph @ 5050rpm @2.0 gearing gets 19% slip
34.5mph @ 3700rpm @ 2.0 gearing gets 18% slip

After 48mph @ 5050 @2.0 gearing gets 23% slip.......Higher pitch increased speed higher hp and lighter weight aka less drag
35mph @5050 @ 2.0 gearing gets 22% slip........Do those numbers reflect less weight (chain loss)

The hull bottom is constant Hp is up 100...where did the HP come from cam or displacement what was the cam duration????
Its seems you now have the torque to swing a larger wheel no speed gain higher slip and if i read this thread right that came from (speed) less bow weight how much did the chain weigh???

The porpising this is a new thing is it not?

Trying to figure out where to start the head (engine) or the tail (prop/drive)

He is giving up a bit too with the XR upper vs. the standard upper he had before.

Have you tried adding ballast to the stern to get back some of the weight you lost and see how it reacts?

I think at this point its about fundamental's tweaking comes later but that is just a opinion.

Slight difference, trim tabs all up for WOT
Before 5200 at 46mph with 2.0 drive and 24 pitch prop

After 5050 at 46mph with 2.0 drive and 26 pitch prop (up 100hp)

Mid range (34 to 35mph) about the same around 3600rpm before or after

Don't know what the cam is, just that I had to raise my risers 3 inches, use longer runner, and do away with silent choice do to possibility of reversion

Proposing is just that now the trim is real touchy and takes very little to go from none to having some. It's just different and this could be because all the weight I took out of the stern from soaked foam and wood.

Removing the chain actually got me a solid 46mph and started to barely increase above it, but only ran it a little while and there was no big change so gave it up. Guess 110 feet of 1/4 chain and a 30 pound anchor is around 150 pounds max

Did add a bit more water in the fresh water tank to get the boat more level, but don't have it full, maybe 1/3. This helped a bit at cruise speed slightly from less trim tab.

Throw the 24's back on. That motor needs to be turning more RPM at WOT IMO.

The cam duration is fairly important i am sure well maybe sure you have moved the powerband up just how far up is the question. It could very well be you have less torque at 3600 with the new motor and cutting off peak hp at 5050 rpm it sound like your close to reversion...just part of the puzzle. At 35mph how much of the hull is in the water and at wot how much does she lift. Simply stated if you were to cut half of the paint off you hull bottom at 35 mph would the hull ride on gelcoat or paint.

http://www.grumpysperformance.com/Du...Manifold01.jpg

I think I need a different prop, one that has more bite. My 24 were slipping bad and the 26 is worst. The more pitch the more slip. If I have a prop that had better bite I might be down to a 22 and more lift. Tuning props is not my strong suit by any means.

If I did go back to 24 I should over rev at WOT but would come out of the hole better.

According to my print out (bored 502), it shows the peak torque at 617ft lb at 3800 rpm. Compared to the stock 502 my torque is up also a bunch

So you are needing cup added to your existing props since standard BIII's have no cup. If you were closer I'd throw my 25 XR's at you to try. Well, hand them over not throw! :flag:

I I have heard this for years but recently soda blasted all the bottom paint off my boat, sanded the hull perfectly then painted it with a 2 part epoxy teflon hull paint and gained 0.000 mph. There were no other changes except the hull paint and we confirmed there is no hook in the hull. I dont think there are enough true life examples to support the theory of bottom paint slowing you down. Maybe with a fat sail boat or a full cruiser but mine is a sporty day boat and the difference was zilch

Knot what is the expected changes from adding cup? maybe thats what I need and I happen to be right next to the best prop shop in canada

You did an amazing job on yours, well done, how is it to tow with a 1500 truck?

I would take you up on that to. Had a set of 22 cupped years ago and the older engine did better but still needed more, so I went to the 24. Only thing I didn't like about the cup is it is more difficult backing up, the props just don't bite. Had to raise the rpm about every time

Then chase the tail so to speak, i am sure BB blades would be more than capable of adding some cup along with some tweaking that would increase bite so to speak, keep one thing in mind you have a lot of blade in the water already 100 more Hp and increased torque and without a weight change your mph has stayed the same...Now if you were running 1000 hp on a 8000lb boat yes you probably could power thru almost any drag that is a fact.

AD, have you verified the new mill is running on all 8 cylinders? Very hard to tell a miss with wet exhaust. I had a plug wire come off once and they only way I could tell something was wrong is that I was down RPM at WOT. That would mess with your slip numbers in the calculator.

Had the computer on it during final onboard tune, had oxygen sensors installed so it one wasn't firing it should have showed up.

Edit: sent bblades and email last night for there thoughts

Well ordered a set of 4x4 from Hill marine at 24 pitch. The big decision to go with Hill, is they did call me back and will also change me out to a different pitch at no cost other then about $30 for shipping each way.

does that mean others didnt call back?

Yes, no return email or phone call nothing. One I called again and they to were in agreement that the 4x4 was the way to go.

Well 8 blades just has to get it done....is there cupping on these multi blade species?

Found out Hill Marine are the ones which actually make the props in house on CNC machines. No cupping but rear prop uses a progressive pitch design. The front and rear prop design is of their design. Talked with "Dad" for about 20 minutes, real nice guy and is a retired teacher. The design was originally made for Yanmar diesels, and was told that if they work they would have a 10K contract (forget if it was a month of year). They then took them to the Miami boat show years ago and have averaged 60 sets a month ever since. Just like Mercs XR props it's my opinion all 4x4's you see folks selling come from hill marine

Interested to hear the results.

http://www.hillmarine.net/Bravo-3-4-...4ds-hpr4cs.htm

^ ^ x 2!

Alldodge, cool to see you ordered a set also. I am probably looking to go to 26s at this point so I have to put a call into Chad today. I got some time in on my 4x4 24s and she pulls on plane pretty hard, faster than ever and to be honest with upping the pitch I doubt I will notice much because she gets up quick at 1/4 throttle. I want to push my cruise up a bit so we will see.

Will be interested to hear how it does with the 26. What does your boat weight?