Need bow lift and more revs for better speed

[Knottymate]

Have 99 Aluminum Fisher Freedom 2000 (Same as Tracker Party Deck) with 150 XR6. Std 19" aluminum gave 5000 RPM at 41 mph. Although sent back to factory with modest improvement (take hook out of hull) as RPM increases from 3800 to 5000 bow noses down with splash line going from just behind drivers seat to in front of seat. Trim up is maxed out just short of cavitating. Engine is one notch up with transom exactly in line with keel bottom

Tried a few SS with now a Mirage Plus 17P . Some help on lifting bow at near max RPM but bow sitll goes down with increasing RPM from 3800 up to 5000.

Any suggestions on possibly a four blade or maybe a better cup prop or engine height or a 15P prop
Note, there is an welded on engine mounting extension about 12" out from the transom this boat came stock with.

 

[QBhoy]

Being honest I don’t know much about these type of boats. We don’t really have them over here in uk.
That said, I have read that amongst others the Enertia, Rev 4 and even fury Props do well on them.
Ive also noted from posts on here that those type of boats seem to be hard to set up well, in terms of engine height and alignment etc.
Someone more familiar will no doubt be along shortly to advise better than I. Good luck.

 

[Grub54891]

Wow. If the boat had a hook in the hull, and was repaired, was it done properly? Did you get the boat new or from someone who got tired of messing with it to get it right?

 

[Knottymate]

The boat was bought new. Had some inkling this was marginal as similar earlier aluminum deep V hulls (Believe called Spectrum) actually small 'winglets' or splash fins welded on the forward V. Very similar to the the fins found on most pontoon boats. Pictures of these boats showed a lot of forward splash line near the forward V. Lowe still makes a boat nearly identical to this boat.

 

[Faztbullet]

If the motor has the original small lower unit that's hurting you on that hull. You need the large diameter 2:1 unit so you can turn a larger diameter prop to hold bow up...

 

[jimmbo]

A prop with more Rake would help in this case, but first... You don't have a bunch of weight, like 2, 3 , or even 4 batteries stashed up front? A bit more weight at the stern would aid your cause. Your engine, does it have one of those god awful whale tails, or some kind of fin thing bolted to the Antiventilation Plate? If so, unbolt and drop/throw it into the deepest water on the lake. The XR6 was not the ideal choice of engine and it does have a gearcase size as, and uses the same prop diameters as the old inline 6s, great for speed on small light fast hulls, but not as good for heavier hulls as the bigger V6 case would have been. Is the transom rigid and has no flex of you were to position your self on the AV plate and bounce up and down? Are the rubber engine isolation mounts in good condition?
Can you provide some pics showing the hull, where it was repaired with a Straight Edge on the repaired area? Also pics showing the relationship between the hull and the AV plate(taken at the AV plate height.
Props like the RAKER, and the Enertia do have higher rake angles, and will lift the entire boat, not just the bow, out of the water. The boat will feel a great deal different.

 

[Knottymate]

Heavens No with the whale tale, 3 batteries and an anchor all in the back. Only trolling motor in front. No pics but can confirm with straight edge engine plate directly in line with keel bottom.

My understanding was factory ''used a power/hydraulic type forming apparatus"" to 're shape' the back end. Note this is
an All Aluminum boat with Stingers hull and siding all aluminum. There are no repair plates/sections etc on the hull

 

[jimmbo]

the factory ''used a power/hydraulic type forming apparatus" to reshape the hull, and unless the hull was braced to reinforce/brace what is now a weakened section of the hull(bent twice), it is like likely to flex again

How much positive trim(out/upward) can the engine provide. I ask because if the engine mount has a large negative angle the engine will not be able to provide much positive trim. Another way I can ask, How much further out can the rim go, after it is parallel to the bottom of the hull?

 

[Knottymate]

Well, it can provide as much as one would want. Meaning I can take the trim up till the prop is out of the water

 

[porscheguy]

A mirage plus is a large gearcase prop. It’s not available for small gear cases. As the sales literature states “it makes big boats go fast.” If he can fit it to his boat I presume it has the more desireable gear case.

The large gearcase version of that motor was available in either 1.87 or 2:1 ratios. Yours likely has the 1.87 gears because 41mph @ 5k rpm would yield a negative slip with the 2:1 gears. With your 1.87 gears, it seems you’ve got 4.5% slip. That’s very good. Almost too good.

one thing I noticed after reading your post for the fourth time is that you said you’ve got a 12” extension which I presume is a setback plate. If that’s the case, you need to raise your outboard height another hole. The farther back the engine is, the higher it can be mounted.

A 17P mirage+ has a 15.5” diameter. You’re moving plenty of water. But if you’ve really got a 12” setback plate, you need to raise the motor another hole.

 

[jimmbo]

The XR6 had a choice of 1.87:1 and 1.78:1 gear cases.

 

[Knottymate]

Thank you folks for all the info. There is a pic attached above of the ''set back plate"' part of the boat from the factory when purchased. Interesting though is my memory with the motor all notches down and stock 19 aluminum the first operating year without factory adjusting the hull boat ran 5200 RPM at 43 mph.

The big problem was the bow drop was considerable with the splash line beginning at the fishing deck. Now with the hull adjustment, 17 Mirage+, motor one notch up the boat splash line is much further back (meaning the hull is out of the water more?). One would thinking there should be more revs and higher speed than new.

 

[Chris1956]

ideally, trim should put the "splash line" even with the transom, or a foot or two in front of it. Back furthest is best. You describe it as being even with front of drivers seat, which indicates boat is not trimmed enough.

150HP on a 20 foot aluminum hull should give reasonable performance. I would stick with a 3 blade prop, but pick one with some rake, and one known as a bow lifter. I would recommend a 17P prop.

You will likely need to do some trial and error measurements with a tach and GPS. With the same load, vary the height of the motor on the transom, and take careful readings at max RPM and trim. Try to max RPM and speed.

 

[porscheguy]

The aluminum prop has more slip. It doesn’t bite as hard and can spin a bit faster.

If the splash line is farther back, then yes it’s because more of the hull is out of the water. Why doesn’t that translate to more speed? For one thing, prop pitch. The 19 will produce higher speeds than a 17 at the same rpm.

I’ve said it before and I’ll say it again, a prop is fine tuning that needs to be done after the basic setup is done right.

Your motor is set so the cavitation pkate is even with the keel. You’ve got a 12” setback plate. The mercury guideline is that for every 12” of setback, you raise the motor 1 inch.

The mirage+ is a great prop. I recommend them a lot due to their reasonable cost new or used, and because of their good performance characteristics. I don’t recommend changing the prop at this time because it’s probably close to where you need it, and you need to get your motor height set to the right level. I’d try the next two sets of holes UP from where it is now. See which ones provide the best result, and only after that should you look at a prop change.

BTW, does your prop have PVS? PVS is the vent system mercury uses on most of their stainless props these days. Depending on the age of yours, you may or may not have it. You can tell if it has the 3 round black plugs on the prop. If you’ve got it, you should consider buying extra plugs in the various available sizes. They allow you to fine tune the prop by adding slip. If you don’t have it, don’t worry about it.

 

[Knottymate]

Thanks Porscheguy for great insight how to proceed which I agree. No PVS.

The only other prop I was considering was the Inertia.

Interesting as I read your message there was a show on the Smithsonian channel with great detail on the Posrche family of cars with complete details on the development of the 911. Know what to buy if they made boats or boat engines.

 

[porscheguy]

I’m not sure if it was Porsche or a third party that adapted a 928 (that’s what I have) 32 valve engine for marine use. Not sure if it ever made it to the water or what the performance was. What I do know is that the 928 engine makes a tremendous amount of torque (300+ lb-ft) and it makes peak torque at 2500rpm. A very usable power range in marine applications. I always give grief to 944/968 owners because they used a 4 cylinder that was essentially half of a 928 engine. It’s sort of like how the 3.0 mercruiser is half of a smallblock Chevy. In the 944 it was 2.5 liters, in the 968 it was 3liters. So I tell those guys their engines aren’t for sports cars, they should be used in boats or small industrial generators.

Its no big deal that you don’t have PVS. The enertia is quite popular, but I would hold off on that until you get the motor height correct.

 

[b.gagnon]

Assuming that the motor is running properly.....
The PVS porting on prop only helps engine rpm rise faster and will not add to the top of the range.. With 12' setback I would think the motor is too low... When the boat is on plane have someone look to see if the anti-ventilation plate is out of the water or plowing through it.

 

[Texasmark]

I only know what I have experienced over my boating lifetime. My first experience with a bow lifting prop was a 1989 Ranger Fisherman with a 115 I6 Merc. The boat had a pad hull just like Ranger's line of bass boats. The prop was a Quicksilver Laser (predecessor to the current Laser II). It had all the amenities of a high performance SS prop including High Rake.

My first trip out I executed the plane like normal but to my amazement the boat came up out of the water and rode on it, not in it, like all my previous boats. As I trimmed out and advanced the throttle, the bow lifted slightly and less and less of the boat was in the water, speed and rpms increased and I came to realize just how high the boat was "over" the water.

Now was it the pad? Was it the high rake of the prop? Probably both running in unison but to get 55 mph out of a new, stock 115 hp engine on a stock 17' boat (with a little chine walk), I was truly amazed. As I recall the prop was 24P on a 2:1 gearbox, don't recall the exact rpms but they were low.

In retrospect I figured the dealer stuck the 24 P on there because he had them for his larger (small gearbox) bass boat engines and it was too much for my rig. I exchanged it for a lower pitch which matched my requirements, dropping my WOT speed but that was OK as I didn't need it nor the chine walk.

So "Need bow lift for better speed" was accomplished for me with the SS prop as I proved it on later hulls, like in my avatar, different rig but Ballistic high performance SS prop with "high rake".

If you want to stay in aluminum, the Turning Point Hustler has all the amenities of SS props except the material and thin blades.....I bought mine on iboats for right at $100. It performed very well when I was in rocky water and didn't want to tear up my SS props. They are thin for aluminum as they use a special formula, but not near razor thin like SS allows.