Props/Performance/Altitude

[keninaz]

I have a Lowe 1467WT (14' walk trough hull) with a Mercury 9.9 HP 4 stroke that I got that way on purpose so that I could use it at Rim Lakes here in AZ where many lakes are restricted to 10 HP or less.
The first run with the boat at my local lake was at 5100' and I could only make about 4.5 MPH as measured via a GPS. The boat with two passengers and all gear included comes it at around 852#. The boat alone is 262# with the walk through and floorboards.
So on Mercury's advice they had me go to a 4 blade 5.5 pitch prop and thought it would help. The RPMs seem to come up higher but there was no speed increase with the same load. Without a tach I think I hit WOT too as the motor cut out a bit at full throttle and the book says this means it's trying to exceed WOT RPM.
Somebody asked me what it does at a lower altitude so today I drove south to Lake Pleasant which is only 1600'. Same load and the factory prop which is a 9 (I think) by 8.5 will do about 6.7 MPH is all. Not fast but OK.
Most of my fishing will be at 5000-6000 on average and I would like to improve performance.
Would perhaps re-jetting of the carb and perhaps a lower pitched prop gain me anything at all or would I be wasting my time?

PS, While at Lake Pleasant which is a good sized lake. I saw a dot some distance from me and it looked like someone standing on water in the middle of the lake. A guy and his wife were stranded and had been there for sometime they said as their jet ski gave out on them. We towed them in but if it had not been for her yellow bikini I might not have seen her. She said they had been yelling at boats and nobody came near them.

 

[Sea Rider]

If you will be fishing always or at around 5100 ft of altitude lakes will need a high elevation jet kit for that height + less prop pitch than standard delivered to better the combo performance, don't expect huge performance with that 9.9, but much better than doing nothing.

Check with Merc dealer if those high altitude jet kits are still awailable, comes in 3K, 6K, 9K ft and so on elevation kits. Besides jets will need to install an induction Hardline or Tiny Tach to tach that engine and check its overall performance. If going back to sea level boating, those high elevation jet kit will make engine to perform awful, will need to install the facory delivered ones back in. Less octane fuel is indicated for high altitude elevations than higher octane ones.

If at sea level wanting a small engine to run top a prop maximization is a must go for, at elevations things gets complicated

Happy Boating

 

[keninaz]

Yes complications do come into the mix for sure. I knew I would lose some 15% of the power at my altitude but the irritating thing about this boat package I bought from Cabela's is that it's supposed to be a Rim Lakes Package meaning it's for fishing the 10 HP or less lakes located at my typical altitude and it's not really setup for elevations. A bit of misadvertising if you ask me. There are quite a number of lake in the mountains of AZ where 10 HP is the limit or electric trolling motor only.
Sounds like a lot of trouble but it may well be worth it. I am not sure what improvement I would see with the jets and prop pitch change but then again this motor have never see anything less than 3700' and may go up to 7000' on a regular basis. I will contact mercury and see if the kits are available. I also just ordered a Tiny Tach The first thing I will do is check the WOT with the 4 blade 5.5 pitch Mercury had me order. If that's OK then maybe the jet kits

 

[Sea Rider]

Very imprudent jet skiers, you should at least go out with a marine whistle to be noted by passerby boats. Don't know how performance will turn out when going to 3 K elevation when jetted for 6 K elevation and viceverse.

Jet kits lets less air and fuel pass into carb for engine to work better, not top though as when jetted for sea level use. Test both props, the standard delivered and the new prop at wot, to check rpm differences with both at 3 K lakes as a starter.

Happy Boating

 

[steelespike]

You have the right Idea just backwards. There is less air at altitude so jets need to be changed to emit less gas.
You need to empty the boat keep only you and legal requirements. Check the wot speed,adjust trim for the best speed and remind us of the
Prop size for each test.Without the empty boat low altitude test we can't really evaluate your motors performance.
On a light reasonably fast boat the motor would make about 20 mph.
I would think it would plane fairly easily and make 12-15 mph. at 1600 ft.
The motor will lose about 3% for each 1000 ft and thats if you do install the kit.
Probably pick a kit that will be very close to your favorite lakes.
You don't want to run too lean if you go to a lower elevation.
If you had an older 10 or 9.9 with adjustable jets you could make any elevation.

 

[keninaz]

Empty the Boat? Really? The boat is rated for a 20 HP motor and 1005# of people and stuff. Other than the trolling motor and battery which are just over 100# there are just two of us in the boat with basic gear.

 

[fishrdan]

The boat is rated for a 20 HP motor

That sounds like the problem as the boat is more than likely going to be a dog with 50% of it's hull HP rating, and then you're going up in altitude which will make the problem worse.... Get the tiny tach installed and see what your RPM's are with the 9P and 5.5P props, you may need something in between.

With that combo, I'd try a hydrofoil to see if it can improve your planing speed. Also, move weight forward and out of the stern; fuel, battery(s), gear, etc. Try moving stuff in front of the middle seat for better weight distribution. I have a Stingray Jr hydrofoil on my 7.5 HP Force and it's worth it's weight in gold, pops my 14' jon boat up on plane quickly. I run about 20mph at Lake Mohave and Mead, 11-12 mph and still planing at 5500' , but it's a dog at 8800'. Elevation kills HP......

It may be worth posting over on the Mercury OB forum to see if there is a possibility of doing a carb swap to pick up some HP. I doubt you'll get lucky and be able to swap carbs to pick up HP, but I'd check it out.

 

[steelespike]

At 6.7 its not planing So your saying that removing about 300 lbs from a 9.9 won't help it plane.?
I think that your 9.9 at 1600 ft should plane a 260lb boat with just the operator aboard.
If it won't something is amiss.I'm not saying it will plane at higher altitudes. I think we need to see it plane the boat.
You could get 5 or 6 mph with a trolling motor on the right size and shape hull.

 

[steelespike]

A quick calculation a 5.5" prop at 6000 @ 13% slip = 12.6 mph Can it turn 6000 with your rig at 1600 ft???The trick is to get it to plane
may require sitting more forward.
A 9" prop at 6000 13% slip is 20.6 mph.It's pretty obvious it won't turn 6000 with your rig
The point is to see if the motor is making full power.

 

[Sea Rider]

We all know that at higher altitude there's less air to breath. Probably missed the key word "size jets" the smaller will restringe air and fuel proportionally as opposed to same factory delivered with carb. The issue here is trying to compensate carb to work better with thin air and less oxygen that thins & rarifies worst when boating at much higher altitudes.

When you tach any combo, must be done so with bare empty boat, just diever and the smallest amount of fuel on a wot run on flat no wind water cond. It's just to check if engine is running inside safe min.max wot rpm factory stated for that engine. Then can go from there playing with props, but doing it at high elevations is other story in which at the most will only achieve fast displacements speeds. If not mistaken, won't be able to swap a 15 HP carb for a 9.9 OB, both are different CC engines.

One refference : Currently sell 2 stroke Tohatsu 18 HP OB to Titicaca boaters, told them since purchase one, that engine will work horrible at 12.5 K ft and that will not be responsibel for its poor performance nor factory warranty. As I don't sell high elevation jet kits, these guys have added small pins to lessen the diam of air and fuel jets as to restringe air/fluel flow. Won't be able to plane anything but happy with fast displacement speeds achieved, they don't even bother going for less pitch props to compensate better power loss at that altitude. To each cracy, his own theme.

For pefect high elevation boating will need to use same factory delivered jets and a system that automatically injects same amount of oxygen found at sea level to compensate any given altitude. Some old radial engine Fairchild planes use bottled oxygen to be inyected to carbs when crossing over the Andes Cordillera. So far none has fallen.

Happy Boating

 

[keninaz]

I talked to the dealer today and they think the 6.5" pitch would work better for me but they agree and re jetting is an option but not a good one for what I will gain. The dealer told me that with the two person gross loading of 850 of the boat at 1600 like I was the other day that he would have expected more like 10-14 MPH out of this boat. Needless to say if this motor is not coming up to RPM I will try a lower pitch and if it still doesn't I guess they will have to work on the motor some? Don't want to water ski but my 50# thrust electric trolling motor will get me 4 MPH at any altitude so only getting some 5+ MPH out of the motor which should be an effective 8 HP anyway is disappointing so far.
Waiting for the Tiny Tach to show so I can do some testing.
Most likely going to be here next week sometime but the winds here have been really bad so far this month anyway.

 

[keninaz]

At 6.7 its not planing So your saying that removing about 300 lbs from a 9.9 won't help it plane.?
I think that your 9.9 at 1600 ft should plane a 260lb boat with just the operator aboard.
If it won't something is amiss.I'm not saying it will plane at higher altitudes. I think we need to see it plane the boat.
You could get 5 or 6 mph with a trolling motor on the right size and shape hull.

Removing my wife and the trolling motor and battery might make it plane but then again solo fishing is not what I bought the boat for. If I cannot plane or get decent performance via mods and such I will just get rid of the motor and go all electric with the trolling motor. Over half the lakes up where I am at are restricted to that anyway.

 

[steelespike]

Removing my wife and the trolling motor and battery might make it plane but then again solo fishing is not what I bought the boat for. If I cannot plane or get decent performance via mods and such I will just get rid of the motor and go all electric with the trolling motor. Over half the lakes up where I am at are restricted to that anyway.

The point of the stripped down test is to evaluate the 9.9s performance.
If we are going to get the best we can from the 9.9 we need to be sure it has got it to give.
The 1467 WT looks like a great fishing buddy But not the best choice for high elevation performance.
A stripped 1467 might actually plane at some of the lower elevations.
If we can squeeze out 10 or 12 mph at some of the lakes that could double your speed and actually save fuel, not that it uses that much.

 

[fishrdan]

I agree with SS, need to do some testing (maybe a lot) if you want to solve the problem. Just moving gear around in the boat could have a big impact on performance, couple other tweaks here and there, and you may be pleasantly surprised with the results.

One thing I don't think was mentioned yet was the outboard's tilt pin, what position is it in now and have you tried moving it into the different (3-4) positions? I can add or drop several MPH depending on the which tilt pin holes I use on my 14'er.

 

[Sea Rider]

One thing I don't think was mentioned yet was the outboard's tilt pin, what position is it in now and have you tried moving it into the different (3-4) positions? I can add or drop several MPH depending on the which tilt pin holes I use on my 14'er.

Why would you need to play with trim holes varying speed when all engine manufacturers Owner's Manuals states that best trim is the one that gives boat and cav plate riding parallel to water level once on plane, provided that combo's weight is well deck distributed.

On my lightly loaded 450 combo with state of the art deck weight distributed if going in / out one more hole, from second hole where it achieves best parallel boat and cav plate riding parallel to water level gives awful performance and notorious speed loss.

At high altitudes the only possible way to tweak here and there any engine is going for less carb jets and prop pitch. You can't fight against altitude, just need to optimize carb and prop for better performance. But boating at different lakes is other story compared to a fixed given altitude.

Happy Boating

 

[keninaz]

I have tried all 3 or 4 tilt positions on the trim. I did find that with the wife on the forward seat it gained a little speed. I will test the boat again without the wife on board using both the 5.5 and the stock 8.5 pitch props once I get the Tiny Tach. I will also leave the trolling battery out. But I am fairly large at 227# myself and it is tiller operated.
As stated, if I am not happy with the overall performance I will just get rid of the motor and if required go to dual batteries with the trolling motor. At this point for my purposes with the specified load and high altitude fishing the gas motor just does not do what I expected and therefore does not serve much of a purpose for me. The 10 HP limit with the reduced performance is OK, barely, but not worth the investment in the motor to me.

 

[steelespike]

For the test move the gas forward as far as possible if you still have trouble planing put the anchor in the bow.
Move yourself forward as far as possible. The whole idea is to see the wot performance.
In my opinion the the 9.9 should plane perhaps not brilliantly.
How wide is the boat at the chines?

 

[keninaz]

I will move the gas forward as far as I can. The anchor is stored in a plastic bucket along with the rope in the bow already, always has been. The beam is 67".

 

[fishrdan]

I wouldn't leave the TM and battery behind, take them along while testing, but move them forward. You can always run back to the dock and put them in the car/truck if needed. To permanently correct the weight distribution, you may need to extend the fuel tank's hose and battery wiring for the TM, so they can be moved forward. This may seem goofy, but I have sat on the edge of the seat leaning forward to get the boat to plane when it was struggling, or tossed gear forward, or had the front passenger spin around and face forward instead of backward. Every little bit helps.

How big is the fuel tank, is it full, and what size of battery do you have.

Why would you need to play with trim holes varying speed

You don't, I was just saying it needs to be checked and put into the correct position for max speed.

 

[steelespike]

Absolutely! Every little bit can help or hurt. Moved around and or removed.
I spent 20 minutes searching on You Tube for 9.9 , 8 and even she 6 hp. being operated on 14 ft boats.
Most boats were pretty light but usually had 2 aboard and gear. Speeds were mostly impressive.