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  Twin Outboard Engine: Separation Distance on Transom

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Author Topic:   Twin Outboard Engine: Separation Distance on Transom
jezza posted 03-25-2015 03:09 PM ET (US)   Profile for jezza   Send Email to jezza  
I have recently purchased two 150-HP outboard engines for my 2001 Boston Whaler 23 Conquest. Is this boat a moderate V-hull? The reason I ask is I want to know the correct position and spacing of my twin outboard setup. I read an article, "Twin Outboard Engine Installation on Moderate V hull Boats" by James Herbert [Hebert], and I was wondering if this applies to my boat? Thanks for any help.
Peter posted 03-25-2015 04:30 PM ET (US)     Profile for Peter  Send Email to Peter     
Boston Whaler would be the best source for twin engine mounting specifications for the 23 Conquest.
power2boat posted 03-25-2015 04:56 PM ET (US)     Profile for power2boat  Send Email to power2boat     
I have the old style Outrage 22 with twin 70-HP outboards. Spacing was set at around 28-inch. You need to be able to squeeze between the motors to service them.

ASIDE: [The OUTRAGE 22 is] a little under-powered for folks on flat water, but okay for me. My friend has the same hull with twin 90-HP outboards. [That OUTRAGE 22] sits stern-low in the water. I also have a 1995 Outrage 24 with twin Yamaha 115-HP outboards. These boats [not clear which of the three boats mentioned] were modified with flush, self-bailing decks, full cabins forward, and fuel tanks above deck forward. The transom on the 1995 OUTRAGE 24 was made for twins [with] 25-inch legs. [The 1995 OUTRAGE 24 with twin 115-HP engines] will plane-out at 32-nautical-miles-per-hour on flat water--which is not too often. I have cruised at 22-nautical-miles-per-hour at 4000-RPM with four people, surfboards and gear. Good enough for me.

jimh posted 03-26-2015 01:31 PM ET (US)     Profile for jimh  Send Email to jimh     
My article, "Twin Outboard Engine Installation on Moderate V-hull Boats", was not written specifically for a 2001 Boston Whaler CONQUEST 23, but there is nothing about a Boston Whaler CONQUEST 23 that suggest to me it ought to be exempted from any of the concerns about twin engine installation I raise in the article. When citing my article, like any author, I would appreciate it if the author's name were spelled correctly. Please note that in the article there is a mention of and a hyperlink to a discussion thread for further questions about the article. The article provides a method for calculating the shaft length as a function of the deadrise angle and the distance off center of each engine, so once you determine the deadrise angle you can perform the trigonometry and calculate the shaft length that is appropriate for the hull and the engine separation to be used.

In general the recommended separation distance is based on two considerations:

--a minimum separation dictated by the physical size of the engine cowlings

--a maximum separation dictated by the size of the transom or splash well.

Boston Whaler publishes the recommended outboard engine shaft length for single and twin engine installation for their various boat models. You can consult with them about their recommended shaft length and engine separation for a specific model.

Since you alrelady bought engines of a certain shaft length, you are going to have to choose the separation with regard to the deadrise angle and distance off center for that particular shaft length. Boston Whaler generally recommend a distance a bit greater than ABYC practices, but suitable for the deadrise angle of their V-hulls.

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