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Top speed twin 318bs 30 ft silverton

M

maxxumnys

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"What should be top speed with

"What should be top speed with twin 318's on this type of boat? Picture attached.

Should it plane?

It seems the boat does about 15-20 MPH top speed and max RPM at full throttle is about 2,700 RPM.

Is this normal?

283444.jpg
"
 
I would think that would be cr

I would think that would be cruising speed top end 30-33 if thats the total rpms your getting its low check to see if bottom and props need cleaned if its been in the water a while it will be messy and that will slow you down alot also causing it not to plane yes it should get on plane
 
what kind of max RPM's sho

what kind of max RPM's should I be seeing?

Also there are some adjustments for trim - I am used to trim on my fishing boat with an outboard - but what is typical use for these on my big boat?

The props are a little dirty from being on sea for a few years but no growth. Will minor things on the props change performance that drastically?

The bottom of the boat is clean and without growth.
 
"they should spin up to around

"they should spin up to around 4000 rpm's , as for speed I agree with Fred, should be in the high 30's"
 
If bottom and props are clean

If bottom and props are clean and both engines peak at the same RPMs...I'd take a close look at the pitch of the props. Also what reduction are the trannys? One other thing. Are the back two barrels on the carbs opening? Folks sometimes do very misguided things in an attempt to get another few knots out of a boat or to improve fuel consumption.
 
Any other people getting 4k rp

Any other people getting 4k rpm on a 318 twin full throttle?

Like I said I get about 2700 max rpm on my 30 ft silverton.

Am I way off for some reason?
 
"I would expect at least 4000

"I would expect at least 4000 R.P.M. out of those. WOT rating is around 4400 R.P.M., but I think that is over kill."
 
"4000 RPM WOT = heavily loaded

"4000 RPM WOT = heavily loaded engine
4400 RPM WOT = lightly loaded engine

Max cruise RPM 75 to 80% MAX WOT
Spoke to an engineer at Chrysler marine many years ago on this issue. Engine life a WOT is measured in hundreds of hours. Engine life at 80% WOT (as I recall) 2000 hrs... At 75% WOT climbs to 3000 hrs. (assuming FWC) All these hours assume engine can reach specified WOT RPMS
(closer to middle, the better)."
 
"Then, mine should last foreve

"Then, mine should last forever! We cruise at only 2,500 rpms (doing about 20 mph).

Jeff"
 
"Its not about how fast you go

"Its not about how fast you go, I've found out, it's about quality time on the water. When it's sailing weather ( blue skys, mild wind) we sail on our 22ft Bristol. When we want to fish or patrol the races for our Y/C or the weather isn't all that nice and we still want out on the water... Power boat. We were fortunate enough to have bought both boats at "the right price" :) and live only a few blocks from the marina, year round. BTW, while my present boat has a "non chrysler engine", I had re-engined my last Lancer with a 318 225HP Chrysler... I loved that engine! Bullet proof and utterly reliable."
 
"My buddy Ed Blakey once said,

"My buddy Ed Blakey once said, "Long as I'm on the water, and moving, I'm happy!"" Good attitude.

Jeff"
 
"David,
Here are some facts

"David,
Here are some facts that were rattled off to me rather quickly, from an owner of a 1976 31'. I tried to take notes.
That boat in the picture is either a 28, 31, or a 34 foot.
The 30 foot would have been an Express. (update your profile)
1976 31', engine options were 318/225hp or 307/220hp.
The 360's became a factory option in 1978.
His was the 318's, 2:1 reduction, 18 X 21, 3 blades from the factory.
34 mph @ 4400rpm (He always felt it was under powered / WOT to get up on plane with 8 passengers)
In 86 he repowered with 275hp/360's (360"s were available in 250, 275, & 300 HP)
He ADDED
5k watt water cooled generator
30 gal holding tank
Bimini top
He changed props to 18 X 19, 4 blades & stayed at about the same speed / rpm range, but it was very easy to get up on plane at 3/4 throttle.
Expect about 1.1 MPG

Fred 156-M"
 
"Yes robert all is wonderful o

"Yes robert all is wonderful on the water. But if the boat should do a certain speed and it's not doing what it should then I am probably getting horrible gas mileage.

In any case...

I clocked my current top speed and it is about 20MPH. I do not reach plane and I create a pretty large wake at that speed.

Max RPM is 2700. I am found some records that indicate 16 x 18 x 3 bronze R&L were purchased. This must be the prop info? The props are bronze.

Engines are definitely 318's at 225 hp supposedly. They sound fantastic with vernatone mufflers straight out the back.

Fred - I also researched and noted that I could not find that a 30' was made for this year - but all documentation and the title say 30'. So I believe it is a 31' in actuality but it does not hurt my feelings any so I save a few percent on doc fees, insurance, etc. LOL

Thank you very much for the information above - great post fred.

When the motors are not under load they certainly hit high rpm but I have never pushed them to limit of course without load.

I'm still curious why I can't plane. Ugh. The trim tabs work perfectly and I have tried that route with adjustments.

Any other ideas?

I'm actually on the boat right now - I arranged internet here at the dock."
 
"Absolutely, I agree... my com

"Absolutely, I agree... my comments about enjoying low speed were directed at Fastjeff not a recommendation that your situation is OK... AS matter of fact, IMHO, you have a serious problem. Did you find out what the transmission reductions are? Also, are the back two bbls opening up at WOT???

Why you can't plane... For any given planing hull, there is a minimum speed to plane. And actually planing occurs over a range. At minimum plane (defined at that speed at which water flows cleanly past the bottom of the transom) to full plane, the point at which the bow of the boat drops closer to level the bow is past its own bow wave...

If it's a displacement hull, it will never plane...just dig a deeper and deeper hole in the water as it goes faster.

If the props are too big ( most likely pitch) for the transmission reduction then the engine will be overloaded and max RPMs won't happen.
Different reductions take different prop sizes.
Also... if the back two BBLS don't open, you won't get full HP to the same effect."
 
Yes; that boat should plane IF the motor is running properly. Either it is not, the prop is wrong, or the bottom is needing cleaning.

I suggest you put a timing light on it and see if you are getting full spark advance AND full retard; it's common for the advance mechanism in those distributors to stick. If they stick advanced--and someone times it that way--then you won't get full advane and the motor will be a dog at full throttle.

Jeff
 
Re: Top speed twin 318 30 ft silverton

fastjeff said:
Yes; that boat should plane IF the motor is running properly. Either it is not, the prop is wrong, or the bottom is needing cleaning.

I suggest you put a timing light on it and see if you are getting full spark advance AND full retard; it's common for the advance mechanism in those distributors to stick. If they stick advanced--and someone times it that way--then you won't get full advane and the motor will be a dog at full throttle.

Jeff
Click to expand...

Jeff,

Bottom newly painted, timing has beem done t times but.i.dont know.that anyone was aware of what you were talking about. How can check mechanical advance manuelly? Id like to do that before i start prop shoping
 
Check that your secondaries are opening at full throttle. Easy to do. Boat doesn't even have to be running.

Take the flame arrestor off and push your throttle lever fully forward. Then look down the carb throat and confirm that the secondary butterfly is fully open.

-JJ
 
Re: Top speed twin 318 30 ft silverton

I have the same boat. I get about 15 to 18 knots at 2500 rpm depending on sea conditions. That's normal speed for this rpm range.

If your timing or advance was off, I don't think your engine would be performing normally at 2500 rpm.

It sounds like something is stopping your carb from delivering fuel/air at WOT position.


-JJ
 
they were just rebuilt and they open... It is either Advance timing issue or prop.... But I think the motor is running solid.... I dont think the prop is anmy different then the orginal but i have run out of things to check. No mechanic wants to be bothered with simply due to most of the them only want to fice what they know can be done to make a quick buck
 
If the carbs are opening all the way it's probably the mechanical advance in the distrinutor not working...one of the most common problems on old engines.

Dan
 
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