Bow of Aluminum Starcraft hopping at WOT.

[sutor623]

Okay guys, I have been talking to a few guys about props for my setup. 1986 16' Starcraft Fishmaster Aluminum (Dry Weight 610lbs.) and 1967 Mercury 650 65hp motor. Current prop is 17P aluminum. I think the diameter is around 11", which seems small to me. Rake is probably 0 degrees. It is definately an older prop, and needs to be replaced soon. Clocked in speed-wise around 35mph (although that is GPS and there was some wind that day) and not quite sure of RPMs but I am ordering a tach soon. There were two of us on board, 6 gallons of gas under my console, our seats are about middle of the boat, one battery in the back, and two all the way up front just to give you an idea of weight distribution.

Here are the issues that I am having. Hole shot is okay, not sure if I would pull up a skier or not, but I will soon see. Top speed to me seems great, but the main issue that I am having is "hull hop" where when I hit 3/4 throttle the bow starts skipping up and down to where I have to throttle down big time. Water was like glass. I trimmed the motor one hole at a time, and the only time it would stop doing it was with the motor all the way down. It seems to me like this will increase drag a bit as it is forcing the front of the boat down pretty hard.

So questions are, would a "whale tail" be a good thing to add onto the lower unit? Should I just be happy that the boat sits down when I trim it properly? Would increasing the rake or diameter of the prop change this issue at all? Thanks fellas, I am new to the prop game.

 

[steelespike]

Re: Bow of Aluminum Starcraft hopping at WOT.

While a tail can be effective solving problems I consider it a bandaid over a setup problem.
I think a tach is a good idea before any changes.
I do think your rpm is about right.
When you have porpoising it could be a hull problem usually a bulge or distortion in the bottom near the transom.
What is the rated hp of the boat?
A 4 blade prop will usually add stern lift, may tame porpoising, can improve hole shot stay on plane with less throttle and respond better at the dock.
it may cost a little top end.
Is the antivent plate(just above the prop) about even with the bottom?
You might try some test runs with the bow batteries in the mid section of the boat.
You might have your passenger move forward a little at a time to get a feel of the problem
You can buy or make wedges that can add or subtract a 1/2 notch.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Cool, thanks for all of the options Steele. Luckily the bottom of the hull is in great shape. The boat calls for a 90hp, but oddly the 65 seems to be plenty. The antivent plats is even with the bottom of the boat. I am willing to sacrifice a little top end to add some hole shot, low end torque, and stability, so ya think a 4 blade would be an option? Here is a vid of the boat while trimmed all the way down.

 

[steelespike]

Re: Bow of Aluminum Starcraft hopping at WOT.

Its hard to tell without not being able to see the spray pattern. It does seem that with the batteries near the console
it might be fine at that setting.It does appear your dragging the trolling motor a little and what appears to be an outboard troller might be touching the water.Maybe causing the bobbing as the motor lifts the bow and the motors dip into the water.
At the least they may slow you a little.You sure have a lot of weight at the stern with 2 motors and the battery and the 65.
Your not under powered ,your at about the minimum.but sometimes smaller motor puts a boats speed at a critical point where ideal trim is difficult to get.You sure have a full compliment of motors.
Evern though you have a lot of weight aft the balance seems ok.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Its hard to tell without not being able to see the spray pattern. It does seem that with the batteries near the console
it might be fine at that setting.It does appear your dragging the trolling motor a little and what appears to be an outboard troller might be touching the water.Maybe causing the bobbing as the motor lifts the bow and the motors dip into the water.
At the least they may slow you a little.You sure have a lot of weight at the stern with 2 motors and the battery and the 65.
Your not under powered ,your at about the minimum.but sometimes smaller motor puts a boats speed at a critical point where ideal trim is difficult to get.You sure have a full compliment of motors.
Evern though you have a lot of weight aft the balance seems ok.

Yeah, unfortunately the spray in the back there is because my transducer is set too low. I am getting a new fishfinder soon, so I do not want to move the old transducer, but when I mount the new one it will be closer to the surface. The small kicker is a 4hp and weighs 35lbs. I suppose it could be catching the water and causing the skipping. The video was taken at full downward trim, and I am comfortable with the ride in this case, just want to have more trim options. I had 4 people on the boat including myself a month or so back, with a 72lb. 9.9hp and the 6gallon gas tank in the back. The weight of the two guys up front prevented the boat from porpoising even at a higher trim setting. My speed was still in the lower 30's, which I am completely comfortable with. I'd like to be able to pull a tuber or two with one or two others on my boat at the same time, so I think the 4 blade would be good for that. I mainly use this as a fishing rig, but I am not opposed to having two props, each with its own application. I am willing to toss a little cash at this guy to get what I want, so I am open to any insight from you, as I know you are a reputable member amongst the forums. I wait patiently with open ears.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

You sure have a full compliment of motors.

Hahaha, yeah I guess to the outside eye it sure looks that way, I have been stranded on the water before where it was so windy that the electric motors wouldnt even move me. I never go out on fishing trips without my 4hp kicker anymore!

 

[steelespike]

Re: Bow of Aluminum Starcraft hopping at WOT.

We shouldn't make any prop changes without a reliable tach reading. remind us of prop size and wot rpm and speed.
Your performance seems reasonable but lacks the details. Depending on the specs You would normally select a 4 blade an inch lower pitch. To maintain rpm. But the selection would depend on your rpm.
I would like to varify the grear ratio. If you pull the plugs and mark the flywheel and prop.In gear rotate the flywheel count the
revolutions to turn the prop once. I have 2 ratios 2.00 and 2.30.Need the ratio to be sure the specs in the calculator are accurate as possible. You may want to double check the diameter
11" seems small. Measure from center of the bore to the tip of a blade and double it.
Usually not a consideration as long as we are selecting for your motor.
Just want to be sure the prop isn't throwing off our numbers.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Agreed, I will get the WOT Rpms as soon as I get my tinytach. If my prop didnt create so much vibration at lower RPMs because of imbalance I wouldnt be stressing the prop, but since I need a new one I want to make an educated buy. I have 2 lower units, the one that is currently installed is a 2.3:1 with a 17P prop. The diameter of the prop seems somewhat small, around 11" or so. RPM range for this motor is 4800-5200 (pretty sure)

 

[pootnic]

Re: Bow of Aluminum Starcraft hopping at WOT.

Video looked fine to me, trimmed all the way down,I didn't see a problem.
It might be as easy as putting more weight in the bow for another trim setting but I don't know why you want to.
If it gets rough and you want to get your bow up you be fine.
A tach would be great though.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Video looked fine to me, trimmed all the way down,I didn't see a problem.
It might be as easy as putting more weight in the bow for another trim setting but I don't know why you want to.
If it gets rough and you want to get your bow up you be fine.
A tach would be great though.

Thanks for your input! Yeah she runs fine trimmed all the way down, I just feel that if I can get it to trim up just a bit more, then I will have less bow drag and attain a higher top speed. Just a theory though. Who knows though, the aluminum is so tricky because it is so light. Ill tell you though, I think putting a 90hp on this thing would be INSANE! Cant imagine going much faster as this thing is a kite. I need a new prop either way so I am just trying to get some ideas before I make an under-educated decision.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Okay Steele, I got a tinytach. Now I wanted to post a pic of the hull so you can see why I am concerned with the motor having to be trimmed at the lowest setting. The angle is just crazy.

 

[steelespike]

Re: Bow of Aluminum Starcraft hopping at WOT.

It sure looks trimmed in/down to the extreme.If the prop is 11" it is really undersized. If we haven't measured; do it from center to the tip of one blade and double the result.
If you need a 1/2 a notch trim you can buy wedges or make some.It occurred to me that a couple of number 2 wood shakes
would work.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

It sure looks trimmed in/down to the extreme.

Oh yeah. Well, even 1/2 tab will still keep this guy really undertrimmed. So you think a 17P by 11" diameter is too small? You are probably correct. Plus the prop is binged up. Ill get you some WOT and hole shot runs in about 2-3weeks when I get out onto the water and give you some info. Then hopefully we can figure this out. I just wanted you to see why I was concerned with the porpoising. I just feel like I am adding a ton of drag with the motor trimmed like this.....

 

[Bondo]

Re: Bow of Aluminum Starcraft hopping at WOT.

Plus the prop is binged up.

Ayuh,... You can't get honest numbers, nor honest runability from a Beat up prop...

 

[muskiemike12]

Re: Bow of Aluminum Starcraft hopping at WOT.

I'm going to assume your motor doesn't have tilt and trim. Maybe getting a CMC trim unit will help your situation. I had a 16' mirrocraft with a 70 hp Johnson and putting the CMC unit on my transom really helped my performance.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Ayuh,... You can't get honest numbers, nor honest runability from a Beat up prop...

Agreed, but I need to use what I have to get the closest hypothesis of which way to go on the pitch scale. Hopefully I can get some useable data from this propellor.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

I'm going to assume your motor doesn't have tilt and trim. Maybe getting a CMC trim unit will help your situation. I had a 16' mirrocraft with a 70 hp Johnson and putting the CMC unit on my transom really helped my performance.

Thanks for the input Mike. I am in the market for a CMC, but probably wont get one installed until the off season of this year.

 

[steelespike]

Re: Bow of Aluminum Starcraft hopping at WOT.

Hopefully we can get trimmed up a little. Perhaps you have a 100 pounder that can move around to help balance things.

 

[sutor623]

Re: Bow of Aluminum Starcraft hopping at WOT.

Hopefully we can get trimmed up a little. Perhaps you have a 100 pounder that can move around to help balance things.

Well I have some batteries that I can use for testing. When I was doing my test run, my main fishing buddy and I were in our primary seats. There was 6 gallons of gas under the console, a battery in the back of the boat, small gas motor on transom, and 2-50 pound batteries in the bow. I will be rewiring my front trolling motor to run off of a battery in the front, and the rear trolling motor to run off the same battery (to keep the weight up there. I will also remove the transducer from its present spot because it is also dragging. I dont plan on keeping 3 batteries, so removing an extra 50 pound battery from the front may only add more issues......

P.S. When I had 4 people on the boat, (2 up front and 2 in main seats) the boat ran fine trimmed up to where the anti-vent plate was 90 degrees with the bottom of the boat. I have inspected the bottom 1,000 times, and it is in great shape. No odd humps, bends or bulges.

 

[Tail_Gunner]

Re: Bow of Aluminum Starcraft hopping at WOT.

All that is going on is your prop engine hull combo are at there best. Your right about the motor being tucked in to much its fighting the hull and losing effeciencey. Time to shift weight to the front of the boat....nothing short of that will be effective.

Thats a very flat bottom boat even with the motor tucked you wake is very shallow...Dhadley should know a fix he plays with flat bottomed boats...ID be willing to bet its a weight balance issue. Id would not run a 4 blad
e it will only lift the stern further