Formula 27PC Complete Power plant rebuild

alldodge

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Thinking out loud; With the original power the factory hook was needed to keep the bow down. This boat came originally with a single 330HP 454 B3, 2.0 ratio. The 415HP 502 moved the boat much easier, but still needed slight bit of tab down to get it up easy. Started getting the prop slip and had the bow up using more trim. The factory hook is robbing power as before, but I'm reaching the max speed with the boat.

Now I have more power but cannot get anymore top end because the hook is now the problem. If this is the true problem how should it be fixed. From the pics below you can see the angle, the hook starts about a foot before the stern.

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Here is the area that goes from the about an inch deep to the back.

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Jacked it up
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I do need to reset the bunks on my trailer or get another. The hull starts going up starting about amidships, and since my bunks stay flat on the keel the stern is lifted a tad. Think I should move the outer bunks in as well, been real hard to line it up. With the hook I cannot get in more forward without putting to much load on the outer hooks
 

Fun Times

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If this is the true problem, how should it be fixed?
Hey AD, start with searching online "blueprinting a boat hull" for some added info.

Most times when adding more power doesn't affect overall performance, the problem lies within the boats actual design, or other issues such as hook, rocker weight, X dimension heights, trim angles.
 

tpenfield

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That is not a hook as one might think of it in terms of being defective. It is a lifting surface designed into the hull. My 242 and 330 both have them.

Also, Formula stops the inboard set of lifting strakes a few feet short of the transom on many of their hull designs. These 2 hull features allow for greater speed without the danger of chine walking.

I would keep any bunks inboard or short of the lifting area to avoid a point load.
 
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alldodge

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Thanks Ted, I sent an email to Scott at Formula with the pic.

Ya know it could be I have just reached the limit of the hull without something drastic. The twin engine setup can go faster but also weight more, but they also have more prop blade in the water. If I could find out what that drastic thing is I could either do it or accept it. The thing that is keeping me guessing is the trim function. It now wants to ride flat instead of the more common 20 degree up.
 

alldodge

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Well its been about a year and thought I would update this old thread with some new stuff. Since last time, I've been working with a guy in MO on some props. Have also tried some Hill Marine 4x4 and others. Some of the stuff I was making matters worst. I was trimming up and getting no more speed just more rpm's. This is where I was messing up. For a brief replay, the boat is heavy and before I rebuilt the transom it was about 3 to 500 pounds heavier from water soaked hull.

Thinking that I could just start with the trim I'm use to was also a wrong way to think. I needed to start with a new baseline. So we started by finding where the drive was flat and level with the bottom of the hull. Then we started running different props.

So here are the numbers

These were all done on one day, water calm, no wind, 1/2 tank fuel
4x4 24 pitch, WOT 4900 rpm, 41 mph = 26.37% slip
3x3 22 pitch cupped, WOT 5200 rpm, 45.2 mph = 16.55% slip
3x3 24 pitch, WOT 5000 rpm, 43.8 mph = 22.91% slip

This set done another day
3x3 22 pitch modified, 5200 rpm, 45 mph = 16.92% slip

The last set of props was run at 1/4 tank fuel and almost 3/4 tank fuel, also water tank (20 gallon) full and empty, and there was little change in the speed/rpm/slip numbers. What we learned is that this is a heavy boat and hard to push. Even if I trim up (bump trim), wait a few seconds, bump up again, wait a few seconds to see if speed increases (and it does not). The cupped prop is the way to go, so even though we have a higher slip number, the cupped props keep the props connected.

Plan forward: calling Hill to see if I can exchange the 24's for 22's and see if I can get them cupped. Looking into see if we can find some 3x3 from Merc with a bit larger diameter prop. Also looking into different rakes and cupping to see what can change.

Looks like
 

Pete104

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There is alot of anti-fouling paint on that bottom. Have you thought about stripping that? I know the "hook" is keeping too much boat in the water for what your working for but a smooth bottom has got to improve it. Do you need bottom paint where you are located?
 

alldodge

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Through much research, the "hook" is not actually a hook, its a design by Formula to give more lift on the outer sides. If it was removed there would be stability issues, probably start porpoising. All Formula's are heavy boats, mine is 9500 dry, and this is before gear, fuel and Generator (have one), and all other items. Agree the bottom paint does cause friction and reduction in speed, it is a small issue when dealing with the performance of the hull

Oh and the paint was stripped off about 3 years ago and redone, this is another subject that went wrong by a Formula dealer
 

NHGuy

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My much smaller Formula has that same design at the rear of the hull. Weighs 4000 lbs dry. It was way underpowered so I built up a bigger engine this past winter. It feels faster now, but I have not GPS'd it. Guess I had better check and report back.
From your testing I would consider reducing the pitch or thinning the blades back to get all the rpms your engine will give.
You can decide how much rpm the engine can stand and reduce pitch to get the drive ratio advantage for liftoffs and the additional power found at higher rpms. Or just stay with the 22's and perhaps have them labbed by someone who knows what they are doing. This way you aren't digging in your pocket for another set of props. A lower pitch will likely use a little more fuel but if you are trying to get all she has it might be a worthwhile thing.
I am sure the folks at Hill would have some insight.
 

tpenfield

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Good update on the prop testing . . .

I think 45 mph and 16% slip are your numbers to go with.

Part of the issue is that boat really needs twin engines. IMO, on a heavy cruiser there is only so much you can ask of a single outdrive and I think you have found a limit of some sorts. As I recall the new engine did not reach that much more top end speed than the original engine, even though you had increased the HP by 25%.

By my rough approximation of HP to speed, you should have seen about an 8% speed increase or 3-4 mph with the extra HP. Not sure how you prop testing compares to the original numbers? Didn't you get 47 mph at one point out of the new engine?
 

alldodge

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Yes I did reach 47 with the Hill 24's, but this was by getting the nose to start to porpoise. Figuring as we know that the prop was slipping at 26$ and the rpms were coming up because of it, so the engine was lugging at slower speeds. The cruiser comes up on plane in about 3 seconds, so the 22's are really holding. We did all the runs with the drive level with the hull to determine if the CAV plate was becoming an anchor as it trimmed up. Did a u-tube vid to see how it looked during the same time.


The vid shows the drive is buried and the outer sides do come full out once it gets above 4K rpms.
 
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