200 hpdi on a 18

[bigblockdock]

I have an 18 I'm just finishing up putting a 150 mercury 2 stroker on. I believe it weighs in at 415 lbs. The boat had a 1987 mercury tower of power inline 6, 115 h.p. on it when I bought it 11 yrs ago. top speed was 39 mph turning a 17 " pitch prop at 5500 rpm. wgt was 316 lbs, and when three men (all over 200) got in the back water would start to come in if the weight was to one side or the other. I figure the 150 would be border line in the weight dept. I have seen 18's with 200 but they were mercurys and all 2 strokers. You can always put plugs in the drain holes. I had a 16 C Hawk with a 70 Yammie on it and needed to plug the drains. It was never a problem, The boat was rated for a 70. I just never took it where it did not belong. I would find a lighter 200 if you want the speed but I would also check around to see if the hull can handle the speed as you should be in the mid 50's or better turning a 21 inch pitch prop. A 150 mercury 2 stroker should put you at or around 50 mph turning a 19 inch prop. You would need to go to double steering cables or hydr. steering. a Single cable would not handle the torque of the 200 at speeds over 50 mph. I don't know of a bracket or jack plate would help. either one might increase the effect of the weight of the motor as it moves the wgt. further back. I doubt if the steering cables could make the bend either so hydr. steering would be needed or you could re route the cables out the transom above the battery. You could run into legal problems if something happened and you did not warn a passenger that the boat was over powered before they went for a ride. Butch

[Fr. Frank]

Yup. They're definitely designed to travel pointy end first.

[sailcat]

[img]/images/graemlins/cool.gif[/img]

[Coyote]

Hello Art,
I have the 18ft. with a 93 200 Merc. with the 25in. shaft
that the book says weighs 407lbs.With a 4 bladed ss prop
Iam sure it weighs around 415lbs.I have always had to plug
my scuppers to stop the water from getting in. Moving the
batteries under the console did not help any. I have a 17gal. above deck livewell in front of the motor that I
want to move under the front seat of the console. Iam hoping
when full and nobody in the boat this will at least let the
rain water go through the scuppers when docked.But what Mark
said about having to raise the deck is the only way you are
going to get the scuppers to be self bailing. Also what Mark
said the 200 will push the 18 along QUITE NICELY.

[SEAFARI]

Bob,
That pic looks familiar [img]/images/graemlins/shocked.gif[/img] Looks
like you dont need those spray rails after
all with that kind of lift! [img]/images/graemlins/grin.gif[/img]

Rodney

[sailcat]

Only needed when going slow. [img]/images/graemlins/smirk.gif[/img]

[Ntrain2k]

mr 2trains i got a luminnum bote15 ar 16 foot s my peepaw has a 225 johnston ,a greene one we call theem turtl enjins, can tihs boatfly.i alwaays want a fling boat.yoo know a bunch bout boat.mabe yoo can come to me home and heelp me.mr. chuck me and me peepaw leeving toda coming to yoor home 1 we tri tihs flee marcket.we stayig at a hotell on the whey that has intrenat hooksup.do yoo hav a telphone we keen cal

???

[bigblockdock]

Hey Coyote,
What is the top m.p.h. with the two hundred on the 18. I'm getting 47 m.p.h.(GPS checked) with a 97 150 merc. turning a 19 inch Mirage 3 blade at 5300 rpm. Did you go to double cable steering or hydra. steering?? I'm hearing you are ok with single cable until 60 mph. Were you able to raise the motor up a hole or two. Was thinking of trying that for a few more R's. With two riders I needed to plug the drains also with the 150 which weighs in around 415 lbs. I have a bowmount motor on the front with two batteries under the front of the console. don't know if that is helping or not but the drains are ok when no one is on the boat. the starting battery and the oil tank (3 gal)are in the rear of the boat. Butch

[Coyote]

Butch
I have the 14x20 ss 4 bladed prop that pushes the boat
about 55-57 right at 6000 rpms with very little trim. I
only ran it this hard one time several years ago just to
see what she would do.(no gps) I know I should go with a
21 or 22 inch just to bring my rpms down some buts its
never run that hard anyway. I think I could get 60 if it
was proped right, but thats about to fast for me in a 18ft
boat. Those big SKA boats that go that fast and faster
probably feel like their hardly moving. I do highly
recommend the hydr.steering.The motor is raised up at
least 1 hole,or 2 Iam not sure.

[bigblockdock]

Coyote, That's moving! I'll try raising the motor up a hole at a time and maybe get a few more r's. The rpm for the 150 tops out at 5600, 5300 is a tad low. I had a 93 200 merc on a gambler bass boat, it would turn a 26 inch pitch but the boat would chime walk at about 74. It was a custom prop from NY, 4 blade. Tried everything but solid mounts to get it right, sold it in 95. Try this for your speeds; RPM Divided by gear ratio ( I believe 1.87 for a 200)equals prop rpm, X prop pitch(equals inch per minute) divided by 12 (changes it to feet per minute) X 60 (per hr.)divided by 5280 (feet in a mile) equals your speed, then minus 5 to 15 percent for prop slippage. There is a shorter formula by merc but I cannot locate it right now. My mirage has 7% slippage according to the GPS reading. You are right on the money with your boat so if you got the speed from a speedo, its very accurate. Seems hydraulic steering is the way to go. It's being used on alot of boats now. the cable in the 18 is new but when it gets stiff, I'm switching over to hydraulic. Butch