Cooling and ross over pipes

[woobs]

I`ve never had a boat that used cross over cooling pipes.

And as I`m usually a chikin`chit when it comes to potential reliability issues (like cooking my engine) I would like to get some opinions on this subject.

I understand the theory on HOW they work... but do they really work. I mean if they did, why would any boat have a circulating pump if it didn`t really need it. So there must be restrictions as to the application or use of a boat so equipped with crossover pipes.....

Now, I am looking at keeping weight down in my project boat and the parasitic loss of power on my wee 4.3 to turn a pump is a factor also. I can use an electric pump but, it`s heavier than an alloy circulating pump. Keep in mind this is a sweetwater boat.

Please educate me. Thanks.

[MOP]

No circ pump is nothing new quite a few marine engines came without them relying only on the sea pumps, Cross overs do a good job and give a tiny bit of extra HP.

Phil

[woobs]

relying only on the sea pumps,

You do mean the sea pump in the sterndrive only, right?
Does that provide enough volume/pressure all on it's own?

I've seen other sea pumps that are belt/cam/crank driven but, that seems to negate the advantage of a change in the first place.

So other than the 9lbs of an electric circulating pump there is no other advantage ?

[mattyboy]

the older volvo setups had a crossover with one belt or cam driven pump the drive just acted as a gravity feed pickup. not sure on an alpha with an impellor

[gcarter]

Crossovers work well. The exception is boats w/Alpha drives w/the pump in the drive.
The impeller is quite short and has long impeller blades. In warmer water (not a problem where you live), the pumping rate can be somewhat limited.

[woobs]

Hi George,

Limited pumping rate for a SBC or do you think my little 4.3 would be "hot under the collar" too ?
(I am using an Alpha One Gen I)


My alternative is going to an electric circularion pump with an electric power steering pump as well. I'm told the PS pump steals about 15 Hp.
If I could net a savings of 25 Hp in conservation between the two pumps it might be worth it as the 4.3 doesn't have much to spare. I'll just have to run a big alternator...

Opinions ?

[johnnywhale]

Hi George,

Limited pumping rate for a SBC or do you think my little 4.3 would be "hot under the collar" too ?
(I am using an Alpha One Gen I)


My alternative is going to an electric circularion pump with an electric power steering pump as well. I'm told the PS pump steals about 15 Hp.
If I could net a savings of 25 Hp in conservation between the two pumps it might be worth it as the 4.3 doesn't have much to spare. I'll just have to run a big alternator...

Opinions ?
PS Pump uses only a few horsepower, and only when under a turning load.

[MOP]

Think for one moment! A sea pump supplies the water at a given rate the supply does not change whether or not you have a cross over or a pump. Alphas have always had marginal pumps but they still cooled, they do however have problems with some after market tube style risers supplying enough water to keep exhaust hoses cooled properly. On a few I have had to block the lower discharge openings in the risers to keep the hoses from getting to hot, with all the holes open there was not enough water volume to fill the riser.

[woobs]

So I've spent the past day or so researching this...and here's what I got.

for cost of Hp...

A heavy duty alternatior can take over 8hp at 5300 rpm
A performance circulating waterpump can take 6-7Hp at 5300 rpm. These losses can be 90% reduced by underdriving the pump with a larger pulley.
A (Saginaw) power steering pump can take 7-8 Hp at 5300 rpm (but only under steering load).
There is a parasitic cost of 1-2 hp for the PS pump when not under load.

So, 2-3 Hp at WFO hardly seems worth all the trouble for a boat that is not racing.

On the weight front...

An alloy waterpump is 8 lbs.
An alloy/electric one is 11 lbs.
A crossover pipe is 1lb.
There is virtually no difference in the weight of the stock PS pump and an electric version PS pump.

I could lose 7lbs by a couple days diet :)

Efficiencies....

An avg Alloy/iron circulation pump flows near 100 gpm.
Avg electric circulation pumps flows near 40 gpm.
I cannot get a max flow number for a sterndrive sea pump (it's 4gpm at idle... 800 rpm)

While the amount of water supplied is limited by the sea pump, the path of that water through the system creates resistance and may not cool evenly. Furthermore, this restriction may serve to "back up" the supply from the sea pump. A circulating pump (as a "helper" pump) ensures that the sea pump can work at it's most efficient state and all cooling passeges have adequite flow.

Conclusions....
For a non race application I feel better with things that prolong the life of my motor (like good cooling) so, I will opt for a circulating pump. Which pump depends on installation and that's it. As the PS pump is only 1-2 Hp drag and only causes an issue under load, I will not be concerned with it either. So, this will be a more conventional set up.

[f_inscreenname]

Woobs, that was the same conclusion I came to when building my Biese drag boat. Just wasn't worth the money and time to do it unless I was going to use the boat for drag racing ( it's drag racing days are long since gone by). Pretty much put the same motor I put in all my I/O's. Belt driven sea pump and a circulating pump. Never a cooling issue.