Help Set up a 15ft speed boat with 85hp v4

[spybot]

I intend to do a lot of work over the winter to my boat but i want to get the best out of her i can this season. She will do around 42mph when im in the boat my self but she has a terrible chine walk at 40mph.
She is a Dateline Bikini (similar to ss16 sidewinder) 15 foot weighs around 660lbs./299Kg
The engine is a 1980 Johnson V4 85hp with PT&T. motor weighs 312 Lbs/141Kg
2 x 110ah batteries 88lbs/40kg
I carry 2 x 22lts fuel tanks. when full weigh 100lbs/45Kg
It will normally carry 2 people 320lb/145Kg
She is used on a loch (lake) when im in the boat my self i carry one fule tank next to me. All other times all the weight bar 1 battery is in the transom.
When getting on plane the boat would be near vertical for around 10/15 seconds.
I have since fitted Smart Trim Tabs. The time to plane is around 5 seconds now but she still chines.
I have the engine sitting in the last hole so she is a high as i can get her without a jack plate. Unsure of the prop.
I have one that will be going on her at the weekend. its a 13 3/4 x 15
Hopefully a bit better i know its not a fast prop but will give her a go.
I will take on board all comments Please advise on this here are a few things i need answers for.
Do i have the engine too high ? its in the bottom hole from the top. The claws for a better word that should sit on top of the transom Sits about 2" above it
Should i move all the weight to the front. ??
She defo needs something????
I will try everything to get this boat set up please any ideas i will love to hear

 

[David Young]

I know nothing on what is right or wrong. You need to post pictures of the boat on the trailer with the motor down so the experts on this Forum can look at them. They will be able to tell if your motor is at the right height or not

 

[jbcurt00]

Probably important info:
http://forums.iboats.com/forum/boat...-for-dateline-bikini-similar-to-sidewinder-16

Same boat, correct, Spybot?

 

[ahicks]

Installing a 15p prop on a combo like that is likely going to be a step backward. My concern would be potential to exceed the engine's red line. Before switching props, you need to know what the one that's on it now is doing as far as rpm. If you're running 40+ pretty sure the prop you have on it now has more pitch (maybe a 17p or 19p?). Figuring out what size is on it now would be the next step.

Chine walk is REALLY dangerous! Do not assume you can stay with it. Some hulls are just not designed to go fast. If fast is your intent, thinking you should be looking for a hull with more potential or be prepared for some exhaustive hull testing/tuning/fiberglass work.

 

[spybot]

Probably important info:
http://forums.iboats.com/forum/boat...-for-dateline-bikini-similar-to-sidewinder-16

Same boat, correct, Spybot?

Correct Same boat

 

[spybot]

Installing a 15p prop on a combo like that is likely going to be a step backward. My concern would be potential to exceed the engine's red line. Before switching props, you need to know what the one that's on it now is doing as far as rpm. If you're running 40+ pretty sure the prop you have on it now has more pitch (maybe a 17p or 19p?). Figuring out what size is on it now would be the next step.

Chine walk is REALLY dangerous! Do not assume you can stay with it. Some hulls are just not designed to go fast. If fast is your intent, thinking you should be looking for a hull with more potential or be prepared for some exhaustive hull testing/tuning/fiberglass work.

Ok this weekend will find out the prop size and get the boat out of the water to check engine hieght.
Will try and get a tacho to find out rmp i found a good site all about props so i will see if i can figure out the best one for me. Is the lay out of the boat wrong ?

 

[ahicks]

No, your boat lay out sounds fine.

 

[spybot]

Will stick with the lay out then and get back to you guys regarding the rpm and prop

 

[Texasmark]

Chine walk is REALLY dangerous! Do not assume you can stay with it. Some hulls are just not designed to go fast.

That's my take on it too. When I first bought my 18' Ranger with a 115 Merc I6, I had too much prop. The following is some 30 years old but best I can remember:

The rig was new and most of the engines the dealer was selling were 150 and up. He apparently had a stock of 24P 13+" props for his fast gear case big bores. One was installed on my boat. I know the prop was too much because even though it was a ported Laser (initial Laser before the Laser II came out) and the ports are specifically made to improve hole shot, it was like 15 seconds to get her up with just me and 10 gallons of gas, 2 ea. 27 and one 24 batteries (hull was about 15 degree dead rise at the transom, lifting strakes, offset, and pad). I had Merc. instruments, tach included but forget the numbers on rpm. I do remember top of the recommended rpm band was 5500 and I was way low when I experienced my problem which, when added to the hole shot time told me it was too much (pitch).

As I was approaching 55 on the speedometer (no GPS then) I started experiencing chine walk. If I dropped down to around 50 it went away. Obviously to get to that speed, I was on the pad and had the PTT set to the sweet spot.

After that first excursion, I played around with the boat for awhile, never getting back over 50 and later took prop back and got a 21P Laser. That put me just under 50 and no chine walk ever and a super hole. So, nothing changed, except the speed.....going from 24 to 21 in prop pitch with the same prop essentially isn't going to effect chine walk per se.

 

[preventec47]

There are different diameter, pitch, blade-area/blade-shape prop combinations that will give maximum performance depending on how
you define performance. Do you want the best absolute top speed at the expense of low speed tug or vice versa or the best compromise
of both. Choose your mission objectives before you start making changes and be sure to document the performance of each change
so you can backtrack when needed.

 

[V153]

Choose your mission objectives before you start making changes and be sure to document the performance of each change
so you can backtrack when needed.

And do only ONE thing at a time! (Christ how many times do I have to tell people ...)

 

[V153]

Fwiw that hull sounds scary if it'll chine walk at 40 mph. Sure your steering's tight? Broken motor mount(s) or something worn out in the mid maybe?

Sounds slow too. I have a similar hull: Baja 15ss. That ran 54.8 with a 90hp Evinrude. Turning a 13 3/4 x 23 OMC SRX.

Do everyone a favor and hook up a tachometer. And know for sure what kinda prop yer swingin. That'd help us out a lot.

 

[spybot]

will do that. I will be at the boat on Thursday hopefully get it done then. At least I will have an idea of what book im on never mind the page