Finally...help please

[nsorvig]

Ok so I finally got down to check out my girfriend's boat (yup she's a keeper!! ) set up and do a little testing. Ok so some background:
*1992 Forester Diva GT 18 ft
*3.0L 4 Cylinder inboard/outboard (OMC Cobra)
*14 1/2 x 19 three blade prop (aluminum)

So I was only getting about 33 mph and 3600 rpm (according to the gauges) and it is really doggy at hole shot but planes out ok. I tried messing with the trim and with it trimmed up a couple inches I got about 37 mph and 4000-4200 rpm (again according to the gauges). it did porpoise a little if I trimmed it up too high. I don't know if the prop for it is right.?. I was thinking about maybe a 4 blade and either a hydrofoil or trim tabs... I think we will probably keep the boat for a few years and then upgrade so I don't want to dump a bunch of cash but do want a little more performance. What are your thoughts??? Any advice helps since this is "my" first boat.

Thanks!!!

 

[ramster]

Re: Finally...help please

SmartTabs will eliminate the porpoising, and bow rise on takeoff, they do work well for little money. As for the prop, you need to spin that motor up to around 4800 rpm with just you in the boat and no gear. I like to be propped right to the max rpm, maybe a little over when empty, that way once you have a full load you still get the revs up close to where they should be. I would try SmartTabs first, as you may be satified with the way boats works after adding them, then maybe switch to a four blade 18 pitch for better hole shot and handling. Keep in mind that a good Stainless prop will also change your rpm's over a cheap Aluminum one. For each inch of pitch you drop, you gain around 150 rpm, but sometimes with a high quality stainless prop of the same pitch you will actually loose rpm. Also, when switching from a three blade to a four blade you usually drop 1 inch of pitch as a rule of thumb.

 

[steelespike]

Re: Finally...help please

My experience a 18' with a 3.0 and a 19 or 21 prop will run around 40 to 40+
at 4600-4800, hole shot a little slow.Of course this isn't carved in stone.
Your rpm and speed seem low to me.Is the motor in excellent tune?Check that the throttle is opening all the way,bottom is clean prop in excellent condition.A compression check is a good idea as well.In the process you can see if the plugs are burning evenly.

 

[nsorvig]

Re: Finally...help please

Thanks for the quick replies! I am going to go get the boat next weekend and hopefully have it looked over and test it out some more. Supposedely my girlfriend's dad checked it out about a year or so ago and it is supposed to be in good working order. I have heard great things about trim tabs. Not such great things about hydrofoils... I should probably just bring it in to get a once over and make sure that everything is working properly and sized right before I start dropping money and new things into it.

 

[nsorvig]

Re: Finally...help please

Ok so some new developments... I found out that the prop that is on the boat (14 1/2 x 19) is not the original prop. I am thinking of switching to the 4 blade 14 1/2 x 18 or something like that and putting on trim tabs. Does anyone know where I can find that factory prop size for this boat (1992 forester diva gt 18 foot with the omc 3.0 liter 4 cyl. engine)? This boat is just going to be used for tubing, knee boarding, skiing and some fishing.

Also any good sites for buying the prop and trim tabs???

 

[Beeched]

Re: Finally...help please

Try right here on I-boats. I got a new prop after I spun my old one. The props here are priced right and the shipping is fast. Quality goods too.

 

[hwsiii]

Re: Finally...help please

Nso, my information shows that manufaturers reomended RPM are 4,200 to 4,600 and your gear ratio is 1.86:1, please verify this. If this is true then you need a 17" pith prop to raise your RPM to 4,600 RPM, and this will inrease your hole shot as well as aeleration throughout your whole RPM range. Usually you should not have muh porpoising from an aluminum prop, but if you will buy the Solas 3 blade prop the porpoising should be very redued.

Prop hange

Iboats Store
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Propeller Specifications:
SKU:#2511-148-17
Manufacturer: Solas
Brand: Amita
Material: Aluminum
Diameter: 14 - 4/5?
Pitch: 17?
Blades: 3
Rotation: Standard (Clockwise)
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[nsorvig]

Re: Finally...help please

hwsiii,
Thanks for the good info! I am slowly but surely learning more and more about these boat things. haha. I was wondering about maybe a 4 blade prop... I hear they give great hole shot and good handling. I plan on pulling tubers, knee boards, joyriding, and of course fishing. I heard the 4 blade only come in even # pitch so would I go with the same diameter and an 18 pitch? Any thoughts?

 

[hwsiii]

Re: Finally...help please

Then this is the prop you need and Iboats has it here.


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Add Amita Aluminum Propeller 2513-145-17 To Your Cart

Propeller Specifications:
SKU:#2513-145-17
Manufacturer: Solas
Brand: Amita
Material: Aluminum


H
Diameter: 14 - 1/2?
Pitch: 17?
Blades: 4
Rotation: Standard (Clockwise)
Usually Ships Within: 1 Business Day