Ballistic with twins?

[Aimrite]

Aloha Net

I am new to this forum and I am looking for some information. Recently I purchased a 6.5 Ballistic for diving here in Hawaii off the South Kona Coast. My wife had one request that I had to honor she said buy what you want but it must have twin engines! What is a man supposed to do? I could not say no!

You see we have no "Sea Tow" here in South Kona and if something were to happen to one of the motors the next island is Tahiti more than a thousand miles away and that is the direction the wind blows.

So I just added to my already too expensive of a boat a set of Yamaha Four Stroke 90's. I know lots of wieght 360 lbs per engine, 720 total. The Dealer assures me it can handle the wieght on the back end so I guess my question is does anyone have any information about this setup or operating a simular boat with an equal powerplant? Prop size maybe, speed, handling in rough water??

Here in Hawaii we say "Mahalo" for Thanks!

Rick

[PeterR]

I would have thought if you were to email Jony at jbt marine he would help but also make sure you have separate fuel tanks and filters.It is a good idea asking around as your dealer may or may not be giving you the best advice and bottom line is it all comes out of your pocket.I do know over here the suzuki,s longterm have a lot less corosion and macanical problems according to a marine engineer freind of mine(Although that is only his veiw)But he does see it from the repair end nor the consumers.Hope that helps.regards Peter

[Roy Smith]

I havant heard of corrosion problems in Yamaha outboards

[PeterR]

Originally Posted by Roy Smith

I havant heard of corrosion problems in Yamaha outboards

Sorry for some silly reason i misread and was thinking it said Honda engines

[codprawn]

Have you considered fitting a bigger single and a smaller aux - say 15hp???

[Aimrite]

Aloha

Yes, I certainly thought about using a single 150 Yamaha with a 15 hp kicker. Typically we are about 15-20 miles offshore and my thinking was although I would be happy with a kicker if that is all I had, however that is a long way to travel on one.

So my options at this point to keep the piece are Twin 60 HP Four Strokes, Twin 90 Four Strokes or possible twin 90 Two Strokes. Although I plopped down a nice deposit on the 90 Four Stokes I am sure the dealer will let me choose the others as well.

I spoke to the Ribcraft Dealer in the US and he said they install twin 90 Honda's all the time on there 6.5's for the military and other government agencies. I have wrote several emails to Asis to ask this question but received no response from the manufacture. I hope this is not an indication of things to come.

Rick

[Aimrite]

Aloha

Just got a phone call from Asis (Dubai) on my cell while here in Japan and they answered the most important question. What they said was although the boat will handle up to 250 hp and Twin 90 Four stroke are no problem for the boat it will run better with twin 90 Two Strokes as it is about 100 kilos less on the back end.

Can anyone get me in the ballpark with prop size??

Thanks!

[yorfuoj]

Aimrite

I am 100% with your wife when she states that she WANTS a twin motor.

I sold a lot of ribs with twin engines, and I was probably one of the 1st in France to do that, ie persuade the customer that 2 is safe, 1 is not !

I sold italian ribs, but most were south-african, a country where nobody takes the risk to go with a single engine. There a white sharks everywhere, so what could you do if your prop starts to slip or breaks ...?

I would strongly suggest a pair of 90-2 stroke like Yamaha - extremely reliable, I had a pair on my own 632 Tomcat - and I fitted more than 15 SA cats with 90 and 50 either.

Yam 90-2stroke not being counter-rotating, you will have to ask - possibly insist - them to be installed with a slight 3° vertical angle - ie not vertical - that is with the point of the V upward.
When this is done, the skegs act like foils.

This is important to get both motors within the same RPM, and avoid the 2xprop torque to push the port pontoon down.
This angle is simply made by drilling the top holes straight in line, like if you wanted the motors vertical, then screwing the motors with 1 hole difference between left and right screw.


On the cats, this angle was 7° (2 holes) - otherwise 6000rpm on right engine, and 5000 on left !


If you choosed counter-rotation, vertical.

Don't be afraid by the statement "with 2 motors, 20% of the power is lost".
This becomes true when you install the max. power allowed by the hull, because the weight of the single becomes much lower than twin.
With 2x90 Yam, your 6.5 Ballistic should reach 40 knots, probably more.
And with those light motors, the dynamic behaviour of the boat will be much better than with 100kg more behind the transom

Should you have other questions, don't hesitate to contact me directly