hard to plane. lack of speed

boatman37

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May 14, 2015
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1,273
hey guys. 1986 sea ray sundancer 250 5.7 merc. put the boat in the water yesterday for the first time. took the kids out today. the first trip we had 7 of us on board. about 1100lbs. plus a full water tank and about 1/2 tank of fuel. the first trip i maxed out at about 12 MPH at WOT. had everyone move up front and still couldn't plane out. took a few people back to the dock and went back out with 3 of us. at full throttle i was able to hit 31 MPH and about 4600 RPM and planed out fine (Sea Ray says this boat maxes out at about 32MPH). went back to the dock and emptied about 12-15 gallons from the water tank. went back out with 3 of us. same result. my speedometer is way off. it read about 15 MPH while one persons phone based GPS read 31. so the last trip we didn't have any speedometer but felt like it was about 31 or so. i didn't try anything less than full throttle. these were only about 1 mile trips up and back each time.

i will say that my prop isn't very good. not sure what pitch, etc but it is dinged up and a small chip off the one blade. i know that has some impact but 12 mph when hauling 7 people? seems pretty normal with 3 or 4 people. the capacity is 10 people 1500 lbs.so not near capacity yet. also, i started with the trim tabs all the way up to try to get full speed

i have another prop like new that i will swap out but need help. might try changing it while it is still in the water.

i also noticed the voltmeter reading about 12 volts while cruising but the last trip was only 11 and my depth gauge was erratic. came back to the dock and realized i left the blower on the whole time. connected my trickle charger to the one battery and it read 12. which leads to another question....i have 2 batteries. 1 new deep cell and one older car battery. i have a 3 way switch and have been leaving it on ALL. what is best practice for battery switch selection?
 

flyingcow

Seaman Apprentice
Joined
May 7, 2015
Messages
36
hey guys. 1986 sea ray sundancer 250 5.7 merc. put the boat in the water yesterday for the first time. took the kids out today. the first trip we had 7 of us on board. about 1100lbs. plus a full water tank and about 1/2 tank of fuel. the first trip i maxed out at about 12 MPH at WOT. had everyone move up front and still couldn't plane out. took a few people back to the dock and went back out with 3 of us. at full throttle i was able to hit 31 MPH and about 4600 RPM and planed out fine (Sea Ray says this boat maxes out at about 32MPH). went back to the dock and emptied about 12-15 gallons from the water tank. went back out with 3 of us. same result. my speedometer is way off. it read about 15 MPH while one persons phone based GPS read 31. so the last trip we didn't have any speedometer but felt like it was about 31 or so. i didn't try anything less than full throttle. these were only about 1 mile trips up and back each time.

i will say that my prop isn't very good. not sure what pitch, etc but it is dinged up and a small chip off the one blade. i know that has some impact but 12 mph when hauling 7 people? seems pretty normal with 3 or 4 people. the capacity is 10 people 1500 lbs.so not near capacity yet. also, i started with the trim tabs all the way up to try to get full speed

i have another prop like new that i will swap out but need help. might try changing it while it is still in the water.

i also noticed the voltmeter reading about 12 volts while cruising but the last trip was only 11 and my depth gauge was erratic. came back to the dock and realized i left the blower on the whole time. connected my trickle charger to the one battery and it read 12. which leads to another question....i have 2 batteries. 1 new deep cell and one older car battery. i have a 3 way switch and have been leaving it on ALL. what is best practice for battery switch selection?



What were the engine RPMs when you were at 12 mph WOT? My first suspicion is that the boat is currently heavier than you think. i.e. waterlogged foam/wood etc. Does the boat have wood stringers? I ran into the same problem on my old boat, and it weighed about 300 lbs more than it was supposed to when empty. The prop could also be contributing. It may not be right for a fully loaded boat, but I'd look into the weight of the boat before changing props.

When I got my "new" boat, it had a battery selector switch. When I was running it, I always had it on both. When I had the motor off, I switched it to 2 (my house battery). I got sick of that and put in a DPST switch from Blue Sea and an ACR. Now it's just on or off.
 

smokeonthewater

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Dec 3, 2009
Messages
9,838
7 people is a bunch of weight... Can't get on plane with as much pitch as w 3 people... That's pretty normal.... A beat up prop is about as good for boat performance as flat tires would be for your car's performance.

Of course try out your other prop BUT don't just guess... Look at both props and find out what they are.... They will likely be stamped ....

Look for something numbers..... Off the top of my head I would want about a 15" pitch on that boat.... It could have a 17" pitch and do fine w a light load but a little less pitch can make a huge difference loaded heavy.
 

boatman37

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May 14, 2015
Messages
1,273
i will check the prop. there is a spare in the boat that the PO says is identical so i will check the numbers on it. i have a SS prop that came with it too but i don't plan on using it. the PO said all 3 were the same. they were a retired couple that i guess was usually just those 2 on it.

if i remember correctly the RPM was about 3600 when i was at 12 MPH.

going to try to figure out which battery is which and mark them. the 'car' battery is anywhere from 2-5 years old. the PO couldn't remember. the deep cell battery is brand new. i just bought it a few weeks ago
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
You need to think logically when using a dual battery switch. First - the voltmeter was telling you something. It was telling you that a) either the alternator is not charging or b) that BOTH batteries were deeply discharged hence the low voltage reading. A properly charged battery will measure 12.6 volts (no load on it) and the voltmeter should read 13.5 - 14.5 volts at anything above 2000 rpm. Next -- since BOTH connects both batteries in parallel, the charging system looks at this like there is one giant battery on-line. With the low voltage reading, why not switch to "1" to more quickly bring the "critical" battery (starting battery) up to snuff. Then switch to '2' to bring the house battery up. You do not need to always run on BOTH. The house battery can be kept charged at the dock by installing a 5 amp or larger on-board smart charger and plug in at the dock. Chances are unless you have a killer stereo system or some other high current draw item on board, you can leave the switch on Battery #1. Most stops are relatively short duration so unless you are anchored for very long periods there is no need to worry about killing a "good" starting battery. Keep in mind also that unless you have a hard to start engine or use incorrect starting procedure, you could start the engine dozens of times before it would kill the battery. So use of the switch i9s very obvious. Set the switch to the battery that needs the most charge. If you cannot remember to turn off the blowers, install a red indicator light on at the helm if it doesn't have one.
 

smokeonthewater

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Dec 3, 2009
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Don't trust the dash volt gauge until you verify that number with a volt meter at the battery....

DON'T EVER run more than a very short time with the engine lugging.... 3600 rpm at full throttle is BAD....

Check the timing on the engine.... Retarded timing will hurt power but the engine will seem to run fine.
 

boatman37

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May 14, 2015
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1,273
i did buy a smart charger yesterday morning. i had it hooked to the new battery and it was reading 100% before we went out. not sure about the 2nd battery. i will hook it up today and also check it with a multimeter.

these were all short 5-10 minute trips. i went about 1 mile upstream then back each time.

if the battery switch is set to ALL and i have the charger hooked to one battery, does it charge both? logic says yes but not sure about that. there is also a good chance that 2nd battery is bad. i will be down at the boat later today but not planning on going out in it. just some cleanup and organizing and just hanging out. but anything else i should check while i'm there? i will try to get the voltage output from the alternator. that was my initial thought anyway.

while at the dock yesterday the only thing running was the refrigerator and as far as i know it was running off shore power. i assumed that because i shut the batteries off and the fridge was running so i guess i had it set to AC. still not sure how to verify that. a dock neighbor told me he shuts his fridge off while cruising and just uses it as a cooler at that point.
 

cptrick3

Petty Officer 2nd Class
Joined
Apr 11, 2015
Messages
157
I have a fairly heavy 24' Chaparral with the same engine/outdrive and on a good day with 2 people on board I can get to about 42MPH (GPS). I have always been told to keep the switch on 1 and both batteries will charge.
 

smokeonthewater

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Dec 3, 2009
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9,838
5 minutes lugging the engine is BAD.... Don't do it anymore.

If it doesn't get on plane in under a minute (preferably way under) reduce throttle and ease along at 1000 rpm or less...
Yes if set to all you would be charging all if connected to any batt.
 

boatman37

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May 14, 2015
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thanks guys. i checked both batteries today and both were at almost full charge. the marine battery was at about 12.7 and the car battery was at 13.1. i had the charger on the marine battery with the switch on ALL.

i looked at the brand new spare prop and its 14.5x17. the PO said it was the same as the one on it. the prop on it now has a chip off the one blade about 2" long and about 1/4" deep. talked to a guy at the dock today that said he will help me change it in the water as soon as it clears up a bit.

according to Sea Ray the top speed on this boat is 32 MPH. i was hitting about 31.5 with 3 of us in it. it planed out pretty quickly with 4 of us on it (about 700 lbs) and 2 of them were at the very back on the bench seat. that was about 420lbs lighter than it was when we could only hit 12 MPH. also, i had the trim tabs all the way up. my thought was that there would be less resistance so it would pick up more speed. but i read that the tabs should have been down to push the front down/lift the rear up?

i didn't even start it up today. just checked things out and hung out and relaxed. still a bunch of debris in the river.
 

smokeonthewater

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Dec 3, 2009
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Yep tabs should be all the way down to help a heavily loaded boat get on plane and then bring em up as soon as it planes out.... That alone will make a huge difference.

Also weight distribution matters.. Don't be too shy to instruct a couple passengers to go up front if need be.

I once had to get a disabled (hole busted in hull) 900cc jetski back to dock so we strapped it on my swim platform... That 500 lbs way back there made my 28'er struggle BAD to get on plane... Had two friends go all the way to the bow and had tabs full down and took prolly 30 seconds to plane...
This boat has twin merc 260 hp v8's and normally pops on plane in just a couple seconds and tops out at 48 mph.
 

boatman37

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May 14, 2015
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1,273
yikes. yeah when we had 7 on board i had 5 of them get up front in the cabin. it helped slightly but not enough
 

SkiDad

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Jul 18, 2010
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I'd be tempted to try a 15x15 prop. Why not try the stainless ??
 

Fly'n Family

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Aug 27, 2014
Messages
6
Tabs down when starting, then up to a proper plane position once planed. They're there for a reason, use them. Someone referenced a bad prop like a flat tire - excellent analogy. If your prop is dinged/bent/out of whack - dump it. Make sure you get the right pitch for your elevation. I run my 370DA at 5600', so I have to use 18 pitch props to hit WOT - where as at sea level it would be 22 pitch props. Keep in mind 1 degree of pitch equals about 200 rpms on average. Also don't expect your boat when fully loaded down with people/fuel/water/gear to hit the same numbers as when lightly loaded - it won't - and don't lug the thing. Mine will hit 28kts with 1/2 fuel/1/2 water and two adults and two kids. This last weekend I had 14 on board and just putted along at 1200 rpms.
 
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