Tower of power!!!! Old starcraft.

[Papafluff]

Hello, newbie here.

I have a 1967 16' starcraft, (Aluminum) closed bow. The boat had 1987 70hp merc on it and I would get 38 on the GPS with 21 pitch stainless.. I recently purchased a mint! 1987 115 inline 6 TOWER OF POWER!! And bolted it on the back of my starcraft ! The boat is rated for a 75hp to give you guys the idea of the size of this boat.

My question is what should I expect for top speed? I'm running the same 21 pitch stainless as on my 70hp merc. I'm curtainly getting 45mph on the GPS! Does this sound right? I'm a lil confused because of such a huge HP increase? Is this the boat design? (She is old) and no matter how much I trim my motor I can not get my bow up! I do have a considerable amount of water spray coming off lower end of motor. I'm knew at this! Any info will help.

Thanks

 

[GA_Boater]

Re: Tower of power!!!! Old starcraft.

Your motor weighs too much for the boat. Of course you know it's too much power too.

 

[Barnacle_Bill]

Re: Tower of power!!!! Old starcraft.

Well besides having the boat over powered, is the motor mounted correctly? (anti cavitation plate even with the bottom of the boat). How many RPMs are you turning at WOT? I imagine you are going to need a pro with more pitch.

 

[Papafluff]

Re: Tower of power!!!! Old starcraft.

The motor only weighs 50 lbs more than the 70 and the boat sits no different in the water. I know the boat exceeds the recommended hp but I'm not the only one who's ever done this. The fact is a lot of hp on a little boat and only 45 mph? The rpms of the motor is a guess at this point (no tach) plan on buying one soon but she is definitely winding up nicely. I plan on buying a 24 pitch but thought even with the 21 I should be getting more than 45mph. The cavitation plate is slightly above the bottom of boat but when the boat is planed out the water catches the front of it causing alot of spray and I'm assuming drag. Is it possible it's the hull design. I would think this motor on this boat should fly

 

[GA_Boater]

Re: Tower of power!!!! Old starcraft.

What model, Nassau?

 

[Papafluff]

Re: Tower of power!!!! Old starcraft.

Yes, it's a starcraft 16' 1967 Nassau.

 

[mercurymang]

Re: Tower of power!!!! Old starcraft.

Got any pics?

 

[Papafluff]

Re: Tower of power!!!! Old starcraft.

I haven't figured out how to post pics yet :-( Totally new here and working from my iPhone

 

[mr 88]

Re: Tower of power!!!! Old starcraft.

Before you buy any props get a tach. A 19" pitch is probably pretty close to red line and they keep pulling a bit after that mark.The tach will get you a base number to work off of.A 1500 L6 on a 15' glass twin tunnel hull weighing in at 425 hit 54 gps on a 20'' prop/ 1" lift-spacer on transom and 6000rpms. You may be over propped which is not a good thing as they like to get wound out,lugging them is not recommended.If so that will also keep your speed down as well..I would guess 48 maybe 50 top speed for that setup propped out right.Not sure about your bow lift issue,got the bow area items/ weight moved to the stern?

 

[wired247]

Re: Tower of power!!!! Old starcraft.

Well besides having the boat over powered, is the motor mounted correctly? (anti cavitation plate even with the bottom of the boat). How many RPMs are you turning at WOT? I imagine you are going to need a pro with more pitch.

Why would you put the anti ventilation plate even with the bottom of the boat? Its only purpose is to prevent air sucking into the prop off idle. Once the boat is moving, the anti ventilation plate does essentially nothing. Putting at the hull bottom point is WAY too low. For a non surface piercing prop all he needs to do is have the prop submerged. The anti vent plate could be 8 inches over the bottom of the hull and it would be just fine. What he really needs to be looking at is where his prop centerline is. My guess is he has the thing way to low right now. 4-5 inches below the hull is a good position for non surface piercing props. TOP's, even with their "20 inch" mid sections, stick that prop way deep for most uses unless its a big boat which his doesnt sound like.

 

[wired247]

Re: Tower of power!!!! Old starcraft.

Too much prop for that TOP. A 19 pitch prop at 6000 RPM will run mid to high 50's. Your motor doent have the stones to push a 24 pitch prop. Also, your motor is mounted WAY too low. Put the prop centerline 4-5 inches below the lowest point of the hull. Forget about the anti ventilation plate.

 

[Papafluff]

Re: Tower of power!!!! Old starcraft.

Thank you all for your quick replies
My boat weighs 525lbs I figured this was light as boats go. I do think I have to raise motor but if I put prop centerline at 4 to 5 inches it would put part of my water intakes and prop above water. I do need to get a tach but I can assure you this motor is screaming with the 21 prop. The boat comes outta the hole like a scalded dog and if your not hanging on I think it would rip the seats outta the floor lol. Is it possible this hull is just no good for top speed? I've read of people getting much higher speeds with much heavier boats but much different hull design than a 1967 starcraft. If I watch the boat go by from shore 90% of the bottom is still in contact with the water no matter how high we trim the motor. I would assume this translates into a lot of drag leading me to believe this boat is just a poor design when it comes to top speed. Any and all info is greatly appreciated and I thank you all for the replies

 

[GA_Boater]

Re: Tower of power!!!! Old starcraft.

The boat is not a poor design when it comes to top speed as you say. You are pushing the design right out the window with too much power and motor weight. You compromised the boat's integrity and the next thing you'll see is popped rivets and cracked chines. It happens on properly powered Starcrafts. Look at the Starcraft restoration threads for an idea.

I have the same tinny, only one year older. The biggest motor I would put on her is about 85 horses, 10HP over. It is very sensitive to stern weight. I wouldn't want to see 45MPH in her, just too skittish. If you want to go faster, buy another boat and put the 115 on it. All of this is my opinion, of course.

 

[wired247]

Re: Tower of power!!!! Old starcraft.

Its a good idea to install a pressure gauge to monitor water pump pressure to be sure but having the prop centerline 4-5 inches below the bottom will still flood the pump intakes. Ive gone as low as 3 without any water intake mods other than putting a set screw in the top three ports. The prop will be fine unless its not then you might need a different prop.

Your boat is plowing through the water because you havent had the power to push the bow up. If the rest of the boat is in acceptable shape ( check the transom ) then the new motor will let you do things you havent been able to do before.

 

[Chris1956]

Re: Tower of power!!!! Old starcraft.

You must get the bow up to gain speed. Some boat hulls run flat in the water, and trim does virtually nothing. Post a picture of the hull.

 

[Papafluff]

Re: Tower of power!!!! Old starcraft.

Yes GA it is your opinion but I value your opinion and thank you for it

 

[Papafluff]

Re: Tower of power!!!! Old starcraft.

I value all your opinions they are greatly appreciated. I will definitely post pics as soon as I figure out how. Working from iPhone any advice? Thank you all for your advice and knowledge should of joined this site a long time ago

 

[wired247]

Re: Tower of power!!!! Old starcraft.

Keep in mind that while your hull is rated for 75 HP that the rating system used back then was the old crank rated system. A 1987 115 TOP is rated using the prop rated system. That would be equivalent to 145 or so HP on the crank system. That rating system was based on a few things such as transom strength etc. but a lot of it had to do with steering and flotation. Make sure that if you 200% overpower your boat ( Like I do ) that it is going to handle the power. Beef up the steering and the transom and make sure that your hull is in top notch shape.

 

[Papafluff]

Re: Tower of power!!!! Old starcraft.


Criss here is a pic of hull

 

[Chris1956]

Re: Tower of power!!!! Old starcraft.

OK, Not the fastest hull design, but should work. Put a straight edge on it, from transom to bow and make sure there is no hook, although, I would not expect one in an aluminum hull. You need to find out why you cannot trim it out and get the bow up. I would presume she plows water as your speed increases?